School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAn evaluation of the role of extension in the Australian pig industry( 1978)Australian agriculture is adjusting to changes in technology, economic circumstances and markets. Extension services as much as the producers' need to change in response to changing industry needs, market trends and consumer demands. There has been much discussion on the problems that these changes present for extension, but none on the basis of empirical research or social science theories. A research program was developed to define the changes taking place in the structure and organisation of the Australian pig industry, and to identify the implications of these changes for pig producers and for extension agencies such as State Departments of Agriculture. The conclusion drawn from the review of the industry situation and from a Delphi survey of 10 experts in the pig industry was that the industry will become more technical and commercialised requiring continual adaptation by the producers to technical and economic changes in order to maintain and increase production efficiency. The survey results showed that a degree of assistance from research and extension was expected by producers to help them maintain and improve production efficiency. Based on the Theory of Personal Constructs, Kelly (1955) an interactive psychological testing procedure known as the Repertory grid was used to record producers' and extension officers' perceptions of each other and of extension services. Twenty pig industry officers, 16 non extension users, 20 extension users and 16 large commercial producers were interviewed. Separate analyses were carried out on the grids of individual subjects, providing profiles of constructs typically used by the subjects in relating to and evaluating people. The results clearly identified the constructs which farmers used in relating to extension advisers and advice. In general, all groups of subjects tended to stereotype people with whom they associated. Combination of both the results within subject groups revealed evidence of commonality within and between the groups in their perceptions. The extension officers saw themselves as progressive and useful while a large number of the producers saw them as theoretical and irrelevant. Extension users held favourable attitudes towards professional agricultural advisers, while large commercial producers and non extension users criticised them on the grounds that they were difficult to communicate with and lacking practical experience. As a group, extension officers were not aware of the questioned relevance of their advice nor of the difficulty experienced by producers in communicating with them. Owing to their practical background and shared experiences, all producers saw other producers as useful and as the most relevant source of advice. The roles they expect him to perform and the characteristics that producers expect from a professional extension adviser have been identified and their implications for the extension officer are discussed. The most obvious implications of the findings are that extension advisers fail to establish the relevance of information within the farmers' context of what is relevant. Based on the findings of the research the theory is proposed that extension programmes will be most successful when producers and extension workers share common perceptions of relevant problems. A philosophy and practice of extension is proposed to meet the farmers' own perception of needs. The interpretation of the results in terms of Personal Construct theory leads to the development of the model of human behaviour, that is, "man as an actor" instead of "man as something being acted upon". A philosophy of extension is developed based on the belief that extension can only be successful if it provides what farmers want. The philosophy states that extension should provide a helping role by facilitating, developing and supporting "man the actor" without dominating or controlling his actions. A practice of extension operating within the boundaries of the proposed new philosophy is developed from the helping relationship model of Carkhuff (1969). The goals of extension are defined as exploration, understanding and action which lead directly to the need for skills which are defined as the "interface skills" of attending, responding, personalising and initiating. The need for and the nature of extension training to provide extension officers with "interface skills" is discussed.
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ItemNitrification and transformations of nitrite in soil nitrogen balance( 1979)Analytical methods were developed to measure nitrogenous gases evolved from soils during nitrification or NO2- transformations. Evolved NO + NO2 is absorbed by an acid solution of potassium permanganate, and the resulting NO3- is determined by a steam distillation procedure. Gas chromatography is used to determine N2 and N20, which are separated on a single column of molecular sieve 5A by temperature programming. Evaluation of closed incubation systems demonstrated that the absorption of NO + NO2 following NO2- addition to a soil, increases with increasing trap : soil surface area and temperature, and decreases with increasing soil water content and depth of soil. Studies of fertilizer N balance and NO2 - transformations required the use of 15N-labelled materials. An apparatus and a procedure were developed to prepare 15N2 for isotope-ratio analysis by mass spectrometry. In laboratory studies, N2, N20 and NO + NO2 were evolved from soils during nitrification of NH3 fertilizer, when soil pH was alkaline. Evidence was obtained to suggest that these losses resulted from chemical reactions involving NO2- . The patterns of gaseous loss in individual soils were very similar to those obtained when NO2- was added to either ?-irradiated or nonirradiated samples. In a calcareous soil, losses were largely prevented by addition of a nitrification inhibitor, which prevented NO2 - accumulation. Nitrite accumulated when pH was alkaline, and NO2 - persistence was related directly to soil pH and inversely to organic C. Gaseous N losses measured in the laboratory did not occur in glasshouse pots treated with 15N-labelled NH3, urea or ammonium sulphate. Possible reasons for this discrepancy are discussed. Studies of the mechanisms of the odenitrification using 15NO2- showed no isotopic dilution of NO + NO2, but N2 was diluted isotopically by approximately 100 percent. It is suggested that NO + NO2 forms through self-decomposition of HNO2, and that N2 may be formed by several mechanisms involving soil organic matter. 15N balance data indicated that another N gas, in addition to N20, was evolved. A significant relationship was demonstrated between the 15N deficit and 15NO2- fixed by soil organic matter. Laboratory incubation and pot experiments demonstrated that NO2- fixed by soil organic matter was resistant to mineralization, but was more readily available than indigenous organic-N. With increasing time, the fixed N becomes more resistant to mineralization. The results of this investigation suggest that champdenitrification may be a mechanism of N loss in fertilizer bands, when Nitrobacter is inhibited. Future avenues of research of the role of nitrification and NO2- transformations in soil nitrogen balance are discussed.
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ItemA study of factors influencing in vitro stability of nitrate reductase from wheat leaves( 1979)This review and the following chapters are concerned predominantly with the processes occurring in higher and lower plants which regulate the amount of NR present in vitro as controlled by degradation, and the level of activity of the existing enzyme. Those factors regulating the synthesis of NR will not be discussed in any detail but only mentioned where they also affect other mechanisms regulating NR. Nitrate reductase is unstable both in vivo and in vitro (101,193, 252). In vitro instability occurs since the isolation of enzymes and other cell components from plant tissue involves disruption of the plant cell. This results in mixing of substances which in situ were rigidly compartmentalized and is likely to result in the isolation of an enzyme which is modified from its native form. Factors present in plant cells which make plant proteins particularly unstable in vitro have been reviewed by Stahrran (216) and Pirie (157). They include vacuole acids, carbohydrates, hydrolytic and oxidative enzymes and phenolic components and their derivatives. In vivo variation in activity occurs in response to a number of other factors, including tissue age (103,129,166,243,264) and environment (15,72,82,1.03,129,261). Tissue age has been shown to influence the activity or stability of NR extracted from a number of species including corn (194,195,264), wheat (221), oats (194,195), tobacco (195) and barley (48). Nitrate reductase has been demonstrated in nearly all plant parts (16) and its ubiquitous presence suggested in higher plants (16,184). Nevertheless, due to the number of factors involved, detection of activity would only occur given suitable physiological and environmental conditions together with use of the correct extraction and assay procedure. Determining if the level of activity derived is an accurate estimate of the in situ activity is even more difficult. This has been attempted by correlating NR activity and grain or plant nitrogen (28, 36) . In vivo instability is indicated by the decline in NR activity with the onset of darkness, depletion of nitrate supply, and water or heat stress (11,82,121,168,235). Under appropriate conditions these factors could also affect the enzyme in vitro.
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ItemThe ecology and physiology of two species of Carduus as weeds of pastures in Victoria( 1977)Slender thistles (Carduus pycnocephalus and C. tenuiflorus) were introduced to Australia about the 1880s. They are now important weeds of pastures in much of southern Australia and are difficult to control with present methods. This study was undertaken to investigate several aspects of the ecology and physiology of the plants with the belief that a knowledge of some of these aspects, particularly of seed germination and seedling establishment, might disclose some "weakness" in the plants' growth which could be exploited to improve control measures. Because of confusion over differences between the two species which occur in Australia the initial step was to evaluate the morphological features which have been used to distinguish between the two species. Although they are very similar morphologically, cytological evidence confirmed that the two species were quite distinct and, in fact, had quite different evolutionary origins. Germination of seeds of slender thistles is controlled by three separate forms of dormancy; these are known as innate, induced and enforced dormancy. Dormancy ensures that the plants will survive in a Mediterranean-type climate and also colonize areas with quite different climates and, most importantly, survive natural catastrophes such as drought, fire, and flood. The germination of slender thistles in the field is confined to a very short period (about 6 weeks) after the autumn break in any year. This is a "weakness" in the plants' survival mechanism because they are vulnerable in that year, at least, to any treatment which can kill seedlings. The herbicide, diquat, was found to kill young seedlings of slender thistles and not affect seedlings of desirable pasture plants associated with the thistles in southern Australia. This treatment is economical and leads not only to a reduction in thistles but an increase of about 30% in pasture production. Several other aspects of the plants' growth were investigated. Slender thistles have early growth characters which give them advantages over more desirable components of pastures. They are more competitive than subterranean clover and ryegrass over a wide range of levels of nutrients, and the traditional approach to pasture improvement in southern Australia of applying superphosphate and sowing subterranean clover will encourage, not suppress, slender thistles. Since grazing animals generally do not eat slender thistles the presence of thistles in pastures at densities commonly occurring in Victoria considerably reduces pasture production.
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ItemBody composition of swamp buffalo (Bubalus bubalis) : a study of developmental growth and of sex differences( 1978)A review has been made of developmental growth and of genetic effects on the body composition of some farm animals. Relationships between chest girth and body weight were studied using sets of data collected in Indonesia from 365 male and 404 female swamp buffalo, each classified to age as having 0, 2-6 and 8 permanent incisors. Linear regressions by which body weight may be predicted from chest girth are presented for each sex-age class. A body composition study, also carried out in Indonesia, was conducted using 12 buffalo bulls and 13 buffalo cows, comprising FBK (Fasted Body Weight; no feed or water for 14 h before slaughter) from 190 to 498 kg or EBW (Empty Body Weight; F minus weight of digests and bladder content) from 158 to 379 kg. Data on HCW (Hot Carcass Weight), HSW (Hot Side Weight), weights of offal components, SMW (Side Muscle Weight) , SBW (Side Bone Weight) , SFW (Side Fat Weight) , SCIW (Side Connective Tissue Weight), weights of SMG (Standard Muscle Groups) and weights of gut tissue components were recorded. The weights of head and tail muscles were also recorded to obtain BMW (Body Muscle Weight) , BBW (Body Bone Weight) , BFW (Body Fat Weight) and BCIW (Body Connective Tissue Weight). The body composition data were analysed by using the variables in the equation: y = axb in logarithmic form (log y = log a + b log x). Comparisons between sexes are being made by using one-sway analyses of co-variance. In the thesis, b values are referred to as growth coefficients or relative growth ratios, and a values as intercepts. (1) Body composition: The apparent and true dressing percentages were not affected by sex and did not change significantly throughout the ranges of FBW and EBW . Both apparent and true dressing percentages are much lower in buffalo than in cattle. At the same FBW or EBN, bulls had less FBW, heavier BBW and BCTW than cows. Bulls had a higher BMW than cows at the same EBW, but both had similar BMW at the same FBW. Sex affected the growth coefficient of head (bulls) cows) and omental fat (cows > bulls) relative to FBW, but it did not affect the growth coefficients of other offal components. Similar results were obtained when offal components were regressed on EBW, apart from the growth coefficient for hide(bulls > cows). At the same EBW, bulls had less blood, heavier head, hide and feet, lighter urogenital tract and alimentary tract than cows. At the same live-weight, the blood, head, feet, hide and alimentary tract appeared to be heavier in buffalo than in cattle. (2) Carcass composition: Sex affected the growth coefficient of SMW relative to HSW (bulls > caws), whereas those for other carcass components were similar between sexes. At the same HSW, bulls had higher SMW and SCIW and lighter SFW than cows (different intercepts), but both had similar SBW. Age (as distinct from erupted incisors) did not affect carcass composition of cows. Within sex comparisons at the same HSW shaved that the buffalo had more muscle than British beef cattle breeds and a similar amount to Bos indicus, Shorthorn cross and Friesian cattle, less fat than cattle, more bone than British beef cattle breeds but similar amount to Friesian cattle and less than Bos indicus cattle.
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ItemVariability in the intake of supplements by grazing sheep( 1979)Although the practice of feeding supplements to grazing animals is widespread through the world, its efficiency still deserves further study. Factors associated with the supplements themselves, the animals being fed, the environment, and the grazing diet being supplemented together constitute a set of variables which affects not only acceptance and intake, but also the nutritional and economic efficiencies of supplementary feeding. This study is concerned with the feeding of supplements to grazing sheep under temperate climatic conditions. Oat grain, hay and molasses-urea blocks (Barastoc, KMM Pty. Ltd., Melbourne) were used initially, but subsequent experiments were confined to the utilization of molasses-urea blocks. Only recently have researchers emphasized the importance of variability in supplement intake between individuals within a herd or flock and estimates of intake, with large ranges between animals, have now appeared in the literature. Langlands and Bowles (1976) considered that such wide variabilities in intake, limit the effectiveness of all forms of supplementation. However, little is known about the factors affecting variability in a group situation and few attempts have been made to identify the possible factors inducing such wide ranges of intakes in grazing animals. Arnold and Bush (1968) identified three types. of sheep: "shy-feeders", periodic non-feeders, and over indulgers". In some situations social dominance has been observed to affect responses to supplements (Franklin and Sutton, 1952; Wagnon, 1965; Squires and Daws, 1975) , and Arnold and taller (1974) correlated the intake of supplements with body weights of sheep. Chapter 1 of this thesis reviews the direct and indirect effects on animal performance of the main factors related to the feeding of supplements. Chapter 2 presents estimations of intake of three supplements, oats, hay, molasses-urea block, made with sheep in small paddocks. Results of behavioural observations and body measurements of the sheep are presented and discussed separately in Chapter 3. Chapter 4 provides an assessment of the acceptability of molasses-urea blocks by seven different flocks of grazing sheep on five private properties. The effects of confining sheep in yards on their acceptance of the blocks are also reported. Few studies have sought to determine whether management stratagems may improve the rate of adaptation of sheep to molasses-urea blocks and induce more uniform intakes between animals. Pilot trials described in Chapter 5 were conducted to identify possible management procedures that may be suitable for these purposes. Four such procedures were sufficiently encouraging to justify testing in a replicated experiment, which is described in Chapter 6. These treatments were imposed on sheep confined in yards and fed hay at a submaintenance levels. The investigations described in Chapter 7 utilised a different approach and are concerned with the behavioural aspects of learning, a topic which has been intensively studied with laboratory animals but only rarely with farm animals. The effects of offering molasses-urea blocks to lambs in the pre-weaning period are assessed in terms of their acceptance of blocks in later life. Inevitably only a few experimental possibilities and combinations have been assessed in the work reported in this thesis. Major attention was directed towards molasses-urea blocks because they induced wider variability in the responses by sheep than did hay or grain supplements . The blocks used were those manufactured by KMM Pty. Ltd., Melbourne, had a hard texture for protection against wet weather conditions and required animals to lick them rather than chew them. Variations in block formulation were not studied in the work described in this thesis and it remains possible that other types of block may have produced different results.
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ItemStudies on the biology and taxonomy of Colletotrichum species( 1978)Studies on the biology and taxonomy of over 350 isolates of Colletotrichum from the temperate and tropical regions of Australia and from southern Florida are presented in this thesis. Many aspects of these fungi, including growth on hosts and in culture, the germination process, sexual reproduction, morphology and soluble protein patterns, have been critically investigated with the aim of finding as many characters as possible with taxonomic value. The reliability of previously used and new criteria for delimiting taxa is evaluated and whether variation in the genus Colletotrichum, as it occurs in Australia, can be satisfactorily fitted into the systematic scheme proposed by von Arx (1957a), 1970) is discussed. The unreliability of host range in delimiting species of Colletotrichum, except its use in cross-inoculation studies, is shown. The finding that host species and organ infected have a greater influence on symptom expression than the identity of the invading fungus led to the rejection of disease symptoms as a taxonomic criterion. The superiority of oatmeal agar in in vitro growth studies of Colletotrichums, especially in cultural comparisons, is demonstrated. For the first time, seta production is established as a valuable taxonomic criterion. The value of growth reaction to temperature as a criterion for delimiting species is reduced by the possible existence of temperature ecotypes which restricts useful comparisons to one climatic region. Studies on germination and appressorium formation have demonstrated that this process is a character of the genus as a whole. Sexual state investigations have helped to explain. the variability in cultural characters of sexual isolates and have shown that sexual characters are generally of little use in delimiting several species. Morphological studies confirmed the value of conidium morphology, providing it is used critically, and established the value of seta characters in delimiting taxa of Colletotrichum. The morphology of appressoria and stromatic structures are also shown to be of taxonomic value. By confirming and extending the results of morphological studies, disc polyacrylamide gel electrophoresis of soluble proteins is strongly recommended as a valuable supplementary aid to such studies. Conidium shape, cultural characters and seta morphoIogy are recommended as the most valuable criteria for delimiting taxa of Colletotrichum. Although variation in the genus Colletotrichum, as it occurs in Australia, can be generally fitted into the systematic scheme of von Arx (1957a, 1970), some modification of this scheme is recommended. The agriculturally important forms of C. gloeosporioides (sensu von Arx), C. lindemuthianum, C. musae, C. orbiculare and C. trifolii, are regarded as separate species, readily distinguishable from each other and from C. gloeosporioides by many criteria. Within C. gloeosporioides (sensu von Arx), several groups of isolates, including Group B, Group C (C. fragariae) and Group E were readily distinguished from other isolates by many criteria and Groups D and F were distinguished by a few criteria. Further work is planned to determine the true status of Groups B, D, E and F. Similarly, within C. graminicola (sensu von Arx) , two groups of isolates were clearly distinguished from each other. The taxonomv of C. graminicola is currently being investigated in a joint project with Dr. B.C. Sutton. In addition, further work is recommended to evaluate the true status of C. coccodes and C. destructivum.
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ItemEffects of growth patterns on body composition and compensatory growth in sheep( 1977)The literature related to compensatory growth in ruminants, with particular reference to sheep, has been reviewed. An experiment was conducted which examined the effects of planned BW losses on growth rate, body composition, wool growth and nitrogen and energy utilisation of sheep when ad libitum feeding was resumed. Sheep were fed a pelleted ration throughout the experiment, and BW loss induced by reducing feed intake. Following developmental growth from 30 to 37.8 kg, Groups B and C lost 21% BW at 122 and 63 gd-1, respectively to reach 30.2 kg BW. Following developmental growth from 30 to 46.7 kg (Groups D and E), Group D lost 34% BW at 125 gd-1 to reach 30.8.kg BW, while Group E lost 23% BW at 157 gd-1 to reach 35.0 kg. Group A was a control group fed ad libitum throughout the experiment. When ad libitum feeding was resumed compensatory growth occurred in treatment groups for up to 10 kg recovery of BW. Group D showed the most persistent increases in growth rate compared with that of control sheep, however, above 50 kg BW there were no significant differences between groups in growth rate. Weight loss did not produce a reversal of the compositional changes which occurred with increasing BW during developmental growth, in the whole body, carcass or offal. However, differences in composition between groups at the end of weight loss were not significant. During compensatory growth there were few differences between groups in the relative growth rates of protein, fat, ash or water in the whole body, carcass or offal. There were some differences between groups in weights of components at specific BW, carcass weight (CW) and offal weight WW), most notably fat and ash. However, these differences appeared to be transitory, and reflected the composition of that portion of the animal at the start of realimentation, rather than an effect of weight loss which was maintained during compensatory growth. The body, carcass and offal composition of sheep appeared to be resilient to periods of nutritional stress, and tended to return to the "normal" composition expected at that weight. The effects of up to 18 weeks severe undernutrition, resulting in rapid BW loss, were able to be overcome during compensatory growth when feed was offered ad libitum. Compared with developmental growth, nitrogen retention increased during compensatory growth. However, the efficiency of ME utilization was not different during these two periods of growth, although DE requirements for maintenance were lower during compensatory growth, compared with developmental growth. Dry matter intakes (DMI) of treatment groups required up to 13 weeks to return to the DMI of sheep during developmental growth, once ad libitum feeding was resumed. Over their respective growth paths Groups A, B, C, D and E required the same amount of feed to reach 50 kg BW. Wool growth rate (WGR) responded more slowly than BW to changes in level of nutrition, both during weight loss and during compensatory growth. There was a lag phase of at least 30 days. WGR during compensatory growth was reduced and required up to 14 weeks to return to developmental WGR after ad libitum feeding was resumed. Total body water (TBW), estimated from tritiated water (TOH) space in sheep undergoing compensatory growth, was overestimated by at least 20%. TOH space was measured without imposing a period of prior starvation on the sheep, and this may have contributed to the large overestimate. Multiple regression equations including TOH space, BW and a maturity factor (M), were able to explain up to 95% of the variation in chemical composition of the body, but residual standard errors were still high.
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ItemSocial and sexual factors affecting reproduction of the domestic boar( 1978)This thesis describes the results of work in three general areas; (i) the influence 0f the social environment during rearing and after puberty on the sexual behaviour of the boar, (ii) the role of the courting behaviour of the boar in his reproductive performance, and (iii) the influence of sexual stimulation on the spermatozoan output of the boar. The major portion of the work relates to the importance of the social environment. Boars reared from three weeks of age in the absence of visual and physical contact with pigs had markedly lower copulatory performance and level of courting activity compared with those reared from three weeks in either an all-male or mixed-sex group. Lack of physical contact with pigs during rearing was responsible for approximately 70% of this depression in copulatory performance. The copulatory performance of boars reared from 12 weeks of age in the absence of visual and physical contact with pigs was considerably less than that of boars reared in an all-male group, but the difference was not significant. Boars reared from three or 12 weeks- of age individually in adjacent wire-mesh pens had similar copulatory performance to that of group-reared boars. However, an apparently important feature of courting behaviour, 'nosing activity', was significantly reduced for those boars reared from three weeks individually in adjacent wire-mesh pens. These data were interpreted as evidence of the importance of social contact, particularly physical contact with boars or gilts, during rearing on the level of sexual behaviour of the boar. In addition to the social environment during rearing, the social environment after puberty was demonstrated to have a dramatic influence on the level of sexual behaviour of the boar. Isolation of post-pubertal boars from female pigs for six weeks significantly reduced their copulatory performance and level of courting activity. The stimuli received from the presence of sexually receptive or sexually non-receptive female pigs were equally capable of maintaining the level of sexual behaviour of the boar. Two experiments conducted at a commercial piggery revealed the importance of the courting behaviour of the boar on reproductive performance. A significant positive correlation was found between the observed level of nosing activity during courting and the conception rate record of the boar. The proposal that the nosing activity of the boar may stimulate one or more physiological mechanisms leading to fertilisation in the sow is supported by the results of the second experiment. Brief courting of sows by a boar prior to artificial insemination significantly increased the farrowing rate and litter size of group-housed sows. Finally, sexual stimulation of boars prior to semen collection significantly increased the number of spermatozoa . in the sperm-rich fraction of the ejaculate. The technique of sexual stimulation of the boar involved either allowing the boar a false mount and then briefly restraining him or allowing the boar to observe a semen collection. The former technique failed to maintain a significant increase in the yield of spermatozoa from the sperm-rich fraction over a six-week collection period. Prostaglandin F2a, which may be involved in the mechanism by which sexual stimulation increases the number of spermatozoa in the short term, was also studied. Administration of 20 mg of PGF2a 30 minutes before collection significantly increased the number of spermatozoa in the sperm-rich fraction of the ejaculate. The experiments of this thesis demonstrate that sexual and social factors have a major influence on the reproduction of the domestic boar.
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ItemHybridization between Lycopersicon esculentum mill. and L. peruvianum (L.) mill( 1979)The incompatibility barrier between L.esculentum and L.peruvianum was shown to be incomplete and to vary for different L.peruvianum strains. The frequency of hybrid production was not increased when both species were grafted on to each other before cross-pollination. Pollinations with L.esculentum pollen followed immediately by L.peruvianum pollen and pollinations with irradiated L.peruvianum pollen also did not increase the frequency of hybrid production. However, using tetraploid L.esculentum as the female parent gave slight increases in the frequency of hybrids produced compared with the cross, 2n L.esculentum x 2n L.peruvianum. Cytological studies of the parent species and their hybrid at various ploidy levels demonstrated close cytological similarity of L.esculentum and L.peruvianum chromosomes and indicated there may possibly be as high a level of chromosome pairing in the diploid hybrid as in both diploid gents. The diploid and tetraploid hybrids were shown to have very high levels of pollen fertility and the triploid to have a much lower level of pollen fertility due probably to chromosome imbalance after meiosis. The results indicate that it would be possible to select within L.peruvianum for strains having compatibility with L.esculentum. It would be most useful to be able to hybridize readily the species at the diploid level because of regular chromosome pairing in the diploid hybrid and a high level of pollen fertility. While the use of tetraploid L.esculentum would slightly increase the frequency of hybrid production, the pollen fertility of the hybrids is low and in a system of back- crossing to diploid L.esculentum, there would be incompatibility between plants having different chromosome numbers