Pollen selection in breeding tomato (lycopersicon esculentum Mill.) for adaptation to low temperature

Summary F₂ and BC₁ progenies from crosses between tomato (Lycopersicon esculentum) varieties differing for growth capacity at low temperature were produced under controlled conditions by hand pollination under two temperature regimes (22°C D/15°C N, normal temperature (N), and 15°C D/8°C N, low temperature (L)) with pollen formed under both regimes, resulting in four pollination treatments: NN, NL, LN and LL. Vegetative growth of the offspring was compared under a rather low temperature regime (19°C D/10°C N). Populations from different treatments within the progeny of a particular F₁ often differed significantly for average dry weight of 7 weeks old plants, the average of the NN population always being higher. Variances for dry weight were sometimes larger for LN populations, but this never resulted from a larger number of vigorous plants. Differences between populations within each progeny seemed to result in part from differences in the conditions for embryo development. Pollen selection at low temperature did not appear to be efficient for sporophyte breeding in this experiment.     

Inheritance of growth characters of tomato (Lycopersicon esculentum Mill.) under low energy conditions

Summary To study the mode of inheritance of W, RGR, NAR, LAR, SLA and LWR, the growth of 15 tomato genotypes and 104 of their F1's was analyzed. The plants were grown at a 19°C day temperature and a 10°C night temperature under a light intensity of 24 Wm^-2 visible radiation and a daylength of 8 hours. Combining ability analyses of variance revealed highly significant differences in GCA values between parents for all characters studied and significant SCA values for some of the characters. GCA values for NAR and LAR, and for NAR and SLA were strongly negatively correlated. A strong positive correlation existed between GCA values for LAR and SLA. The possibilities for improving growth under low energy conditions by using growth characters in breeding are discussed.Abbreviations W dry weight of the plant - RGR relative growth rate - NAR net assimilation rate - LAR leaf area ratio - SLA specific leaf area - LWR leaf weight ratio - MANOVA multivariate analysis of variance - GCA general combining ability - SCA specific combining ability     

Inheritance of characters determining growth and development of tomato (Lycopersicon esculentum Mill.) under low energy conditions

Summary Diallel crosses were made between 15 tomato genotypes with varying performance under a low energy regime. It appeared that differences between genotypes for 11 vegetative and generative plant characters are determined mainly by additive genetic variation. For breeding cultivars adapted to low energy conditions, crossing genotypes with a high GCA for weight of trusses and fruits (WTF) and genotypes with a high GCA for weight of vegetative plant parts (WVP) seems most promising. Complications may arise from the negative correlation between GCA values for WTF and WVP, and the strong positive correlation between GCA values for fruit number and WTF, causing small fruits.     

Inheritance of resistance to fruit rot (Phytophthora parasiticaDast.) in tomato (Lycopersicon esculentum Mill.)

Summary Fruit rot disease caused by Phytophthora parasiticaDast. is a limiting factor in tomato production in Himachal Pradesh. 30 to 60 per cent fruits are damaged by this disease. Crosses were made between EC 54725 (Lycopersicon pimpinellifolium), a small tyuited type, resistant to fruit rot and four highly susceptible tomato commercial cultivars (Gola, Sioux, S12, and Lalmani). Studies of F₁'s, F₂'s and back crosses indicated that EC 54725 carries a dominant gene imparting resistance to fruit rot.     

Inheritance of quality traits in processing tomato (Lycopersicon esculentum Mill.)

Summary The genetic basis of pH, colour and soluble solids in processing tomato is examined. In a first experiment, aimed at identifying the base populations with which to start selection, parents, F₁ and F₂ progenies of an 8 × 8 diallel cross without reciprocals were tested.The results indicate that additive, dominance and additive x additive epistatic effects were noticeable for the three characters. Higher order interlocus interactions were also detected.As to the soluble solids, a trait for which higher order epistatic effects were less marked, the breeding potential of the cross combinations was assessed by calculating the expected mean values at the F generation. Some cross populations having C33 or C35 as parent appeared to be superior.A second experiment was conducted to collect data on the heritability of the foregoing qualitative traits by utilizing the regressions of F₃ offspring on F₂ parents. The low heritability coefficients observed would suggest the ineffectiveness of individual selection in early generations.In both the F₂ and F₃ generations rather low correlation coefficients among the three quality traits were observed.     

Inheritance of tolerance of the tomato (Lycopersicon esculentum Mill.) to metribuzin herbicide

Summary The inheritance of tolerance in the tomato (Lycopersicon esculentum Mill.) to metribuzin 4-amino-6-tert- butyl-3-(methylthio)-as-triazine-5(4H)-one herbicide was investigated. A biossay using a nutrient solution culture in controlled environment growth cabinets was used to evaluate progeny from tolerant by susceptible tomato cultivar crosses for response to metribuzin. Fireball and Vision were used as tolerant cultivars and Heinz 1706 as a susceptible cultivar. Parental, F₁, F₂, and some backcross generations were studied. Visual phytotoxicity, seedling height, and seedling dry weight were recorded.The bioassay was effective for classification of the segregating generations. F₂, and progeny variance analysis suggested that the inheritance of tolerance to metribuzin was controlled by one major gene with modifiers. Heritability values of 0.58 to 0.72 indicated a potential for cultivar improvement through plant breeding.     

Effect of three anthocyaninless genes on germination in tomato (Lycopersicon esculentum Mill.) I. Seed germination under optimal conditions

The effect of three mutant genes affecting anthocyanin biosynthesis – anthocyaninless of Hoffmann (ah), anthocyaninwithout (aw) and baby lea syndrome (bls) – on tomato germination capacities at 24 ° C was investigated. The study was performed on nine anthocyanin containing lines – Apedice, Apeca, Ailsa Craig, Monfavet 167, Monfavet 168, Por, Piernita, VF 36 and VFNT cherry and 13 isogenic/near isogenic lines (IL/NIL) from them: 4 differing for gene ah, 3 differing for gene aw and 6 differing for gene bls). In the majority of the anthocyaninless IL/NILs germination began earlier than that in the wild type lines. Significant differences were observed in the time to 50% germination between the anthocyanin-containing and the anthocyaninless IL/NILs except for the most rapidly germinating line VFNT cherry. Seed weight, water uptake, effect of testa removal and presence or absence of maternal effects in F1 germination responses were investigated in order to elucidate the causes of the more rapid germination in the anthocyaninless IL/NILs. The increased amount of water uptake by the anthocyaninless lines, the shorter treatment time necessary for their testa removal, the important maternal effects in the genetic variability of the time to 50% germination and the differences in germination capacities between the wild type and the mutant IL/NILs after testa removal, indicated that the seed coat and the endosperm had to be affected by the effects of the three genes in a way that caused enhanced germination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-temperature-related growth and photosynthetic performance of alloplasmic tomato (Lycopersicon esculentum Mill.) with chloroplasts from L. hirsutum Humb. & Bonpl.

Growth and photosynthetic performance were analyzed in alloplasmic tomato at a high- (25/17 ^°C; HTR) and low-temperature regime (12/6 ^°C; LTR) in order to establish the role of cytoplasmic variation on low-temperature tolerance of tomato (Lycopersicon esculentum Mill.). Four alloplasmic tomato lines, containing the nuclear genome of tomato and the plastome of L. hirsutum LA 1777 Humb. & Bonpl., an accession collected at high-altitude in Peru, were reciprocally crossed with 11 tomato entries with a high inbreeding level and a wide genetic variation, resulting in a set of 44 reciprocal crosses. Irrespective of growth temperature, alloplasmic families with alien chloroplasts of L. hirsutum (h) were on average characterized by a high shoot biomass, a large leaf area, and a low specific leaf area in comparison with their euplasmic counterparts. These results do not directly point to an advantageous effect of h-chloroplasts on biomass accumulation at low temperature but rather towards a small general beneficial effect on growth and/or distribution of assimilates. Significant chloroplast-related differences in photosynthetic performance, however, were not detected at both temperature regimes, indicating that h-chloroplasts can properly function in a variable nuclear background of L. esculentum. It is concluded that chloroplast substitution is not an effective method for breeding tomato plants with improved low-temperature tolerance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of tomato cultivars (Lycopersicon esculentum) by polyacrylamide isoelectric focusing

Summary Isozyme analyses have been used for the definitive identification of many plant cultivars, but not for cultivated tomatoes. Six isozyme systems, namely alcohol dehydrogenase, acid phosphatase, phosphoglucomutase, esterase, phosphoglucoisomerase and 6-phosphogluconate dehydrogenase of tomato seed extracts were resolved by isoelectric focusing on polyacrylamide gels with a narrow pH gradient. Nine alcohol dehydrogenase phenotypes were distinguished which, with three acid phosphatase phenotypes, identified twelve of the seventeen cultivars. Fewer differences were found for the other isozymes. Since this method could differentiate between breeding parents and their progeny it is concluded that further investigations are warranted.Abbreviations APS acid phosphatase - ADH alcohol dehydrogenase - EST esterase - IEF isoelectric focusing - PGI phosphoglucoisomerase - PGM phosphoglucomutase - 6-PGDH 6-phosphogluconate dehydrogenase - RFLP restriction fragment length polymorphism - VOPRI Vegetable and Ornamental Plant Research Institute     

Effects of CO2 enrichment on young plant growth of 96 genotypes of tomato (Lycopersicon esculentum)

Summary The early growth of 96 genotypes of tomato was studied at 320 ppm CO₂ and at 750 ppm CO₂ in separate climate rooms. Plants were harvested at 40 and 55 days after sowing. Fresh and dry weights were determined. Large differences between genotypes were found for average plant fresh and dry weights and for relative growth rates. The average overall growth enhancement by CO₂ enrichment was 2.3. Two genotypes showed significant genotype x CO₂ interaction. The consequences of these results for tomato breeding are discussed.     

Genetics of resistance to early blight (Alternaria solani Sorauer) in tomato (Lycopersicon esculentum L.)

The genetic nature of early blight resistance in tomato was studied in three crosses at seedling and adult plant stages. A six generation mean analysis of the cross Arka Saurabh (susceptible) × IHR1939 (resistance) and its reciprocal cross revealed that the resistance to early blight was conferred by recessive polygenes at both seedling and adult plant stages. This polygenic early blight resistance revealed the importance of additive and additive × additive gene effects at seedling stage and higher magnitude of dominance and dominance× dominance gene effects at adult plant stage. Evaluation of parents, F₁, F₂ and backcross generations of IHR1816 (resistance) × IHR1939 (resistance) revealed that the early blight resistance genes in IHR1816 (Lycopersicon esculentum NCEBR-1) and IHR1939 (Lycopersicon pimpinellifolium L4394) are independent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Overcoming unilateral breeding barriers between Lycopersicon peruvianum and cultivated tomato,Lycopersicon esculentum

Summary Treatment of Lycopersicon peruvianum stigmas with an artificial medium analogous to stigmatic exudate allowed pollen germination and growth on immature pistils. Growth of Lycopersicon esculentum pollen tubes to L. peruvianum ovules, an otherwise incompatible cross, was achieved following such treated bud-pollinations. No plantlets were recovered, although a few embryos from this cross at the globularity heart stage of development were excised at 22 days after pollination, indicating the presence of crossing failures as severe as in the reciprocal cross. Hybrid plants were obtained from the reciprocal cross, using as pollen parent an L. peruvianum line selected for congruity with L. esculentum. Bud pollinations to L. peruvianum, using these interspecific F₁ hybrids as the pollen parent, allowed viable embryo development and plantlet recovery. Resulting backcross plants, which possess approximately 1/4 L. esculentum genome in a L. peruvianum cytoplasm, may facilitate further introgression of the L. esculentum nuclear genes into in foreign cytoplasm.     

Phenotypic,genotypic and environmental correlation in tomato (Lycopersicon esculentum)

Summary Twelve inbred lines of tomato and their 132 hybrids (reciprocals were considered separately) were studied in four environments: glasshouse and open air, with and without plastic cover. Nine characters were recorded and the phenotypic and environmental correlations between them were obtained within environments and for the complete set of data. Characters showing the highest phenotypic correlation with yield were fruits per cluster and earliness in harvesting, but neither of them is useful for indirect selection for yield. To the contrary, leaves between racemes can be used when selecting for fruits per cluster. Environmental correlations were generally low, excepting total yield in fruits per cluster.Broad sense heritabilities were obtained, which were rather high for fruit weight, locules per fruit, fruits per cluster and leaves between clusters. Some cases in which phenotypic correlations were rather constant for the different environments in spite of the great differences recorded for the genotypic correlation coefficients, are explained because of the great weight (i.e., considering heritabilities) of environmental correlations on phenotypic correlations.     

Inheritance of net photosynthesis,dark respiration,stomatal resistance and related characters in tomato (Lycopersicon esculentum Mill.) under low energy conditions

Summary Inheritance of net photosynthesis, dark respiration, specific leaf fresh weight, and stomatal resistance was studied in a diallel cross without reciprocals with 15 tomato genotypes. The plants were grown under low light intensity (24 Wm^-2), short days (8 h) and low temperature (19 °C/10 °C day/night temperature). Significant f-values for GCA were observed for all characters. Smaller, but for most characters also significant f-values for SCA were found. This indicated that the characters were mainly controlled by additive gene action. The relationships between the physiological characters and breeding aspects are discussed.     

Effect of three anthocyaninless genes on germination in tomato (Lycopersicon esculentum Mill.) II. Seed germination under stress conditions

Seeds from four pairs of tomato isogenic/near-isogenic lines (IL/NIL) differing for anthocyaninless of Hoffmann (ah), three pairs of IL/NILs differing for anthocyaninwithout (aw) and six pairs of IL/NILs differing for baby lea syndrome (bls) were evaluated for their germination ability under stress conditions: low and high temperature, salt and osmotic stress. Mutant genes affecting anthocyanin biosynthesis enhanced tomato germination capacity under all above mentioned treatments, except for the aw gene under a PEG-6000 treatment. Testa removal accelerated germination under stress conditions, but differences in time to 50% germination between the wild type lines and their ah-, aw- and bls-IL/NILs although diminished, were not eliminated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of low-temperature tolerance during germination in tomato, Lycopersicon esculentum Mill.

The genetic basis of low-temperature tolerance during germination of tomato seed was investigated using two approaches. First, a cold-tolerant (PI 120256) and a cold-sensitive tomato cultivar (UCT5) and their reciprocal F₂, F₃ and BC₁ progeny (total of 10 generations) were evaluated for germination at a low (11 ± 0.5°C) and a high (control) temperature 20 ±0.5° C) Weighted least-square regression analysis indicated that in the low-temperature treatment most of the variation resulted from additive genetic effects, and dominance and epistatic interactions were nonsignificant. Partitioning of the total genetic variance into those attributable to the effects of embryo, endosperm, testa and the cytoplasm indicated that additive effects of endosperm and embryo could individually account for 80% and 77% of the total variance, respectively. In the control treatment, greater than 60% of the variation could be explained by individual additive effects of endosperm or embryo and ? 27% of the variation could be explained by embryo dominance effects. Across generations, there was a positive correlation (r = 0.78, P < 0.01) between germination in the control and low-temperature treatments and there were no significant genotype × temperature interactions. The results indicate the presence of similar or identical genes with predominantly additive effects on germination under both low and high temperatures. In the second approach, the effectiveness of directional phenotypic selection to improve tomato cold tolerance during germination was evaluated by selecting (in an F₂ population of the same cross) the fastest germinating seeds under low temperature and comparing the germination of the selected F₃ progeny with germination of an unselected F₃ population. The results indicated that selection was highly effective and significantly improved germination performance of the progeny; a realized heritability of 0.74 was obtained for low-temperature tolerance during germination. It is concluded that in these tomato lines germination under low temperature is genetically controlled, with additivity being the major genetic component, and thus the trait can be improved by phenotypic selection.     

Introgression of in vitro regeneration capability of Lycopersicon pimpinellifolium Mill. into recalcitrant tomato cultivars

The goal of this research was to study the introgression of the high regeneration capacity of Lycopersicon pimpinellifolium Mill line WV-700, in recalcitrant tomato cultivars (L. esculentum Mill cvs. Petomech, Santa Rita and VFN-8) using backcrossing. Hypocotyl explants of in vitro germinated seeds were cultivated in half strength MS medium supplemented with 5mg/l 6-BA to assess their shoot regeneration capacity. The apical shoot of the in vitro germinated seeds were cultured on a separate medium. Apical shoots from genotypes showing high regeneration rates were acclimated in a glasshouse and used as pollen donors for the next backcrossing. After four backcrossings, the material showed a similar mean fruit weight for the cultivated tomato and a high regeneration capacity similar to the wild species. It is shown that L. pimpinellifolium can be used with success as donor parent to introgress in vitro regeneration capacity to recalcitrant tomato cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pleiotropic effects of male sterility genes in hybrid tomatoes (Lycopersicon esculentum Mill.)

Summary The influence of seven recessive male-sterile alleles on early marketable yield, total marketable yield and average fruit weight in heterozygous F1 hybrid tomatoes was studied. Differences were found between nearisogenic F1 hybrid pairs, in the mutants ms-14, ms-17 and ms-18 for percentage of early marketable yield; in the mutants ms-17, ms-31 and ms-47 for average fruit weight; and in the mutants ms-14, ms-17 and ms-33 for total marketable yield. These differences may be attributed to pleiotropic effects of male-sterility alleles or genes highly linked to these alleles. The direction and the magnitude of the pleiotropic effect on a specific characteristic were found to be dependent on the general genetic background of the parental lines and the specific combining ability of the F1 hybrid. Interactions found in crosses between male-sterile and male-fertile female lines and parental lines suggest that male-sterility alleles affect the general combining ability of female lines. Such differences were demonstrated to be statistically significant for percentage of early marketable yield with mutant ms-18, for average fruit weight with mutants ms-47, and for total marketable yield with mutant ms-17 and ms-33. The absence of uniformity with respect to the pleiotropic effects and occasional deviations in the general combining ability are discussed.     

The effect of the lateral suppressor gene on seed germination in the tomato

Summary A reduction in germination of tomato seed due to the lateral suppressor mutant (ls) is demonstrated. This is shown to be an effect of the maternal genotype rather than of the embryo. Poor germination is not determined until comparatively late in seed development and the effect can be avoided by embryo culture. Cuticular necrosis of the mutant seed appears to be associated with poor germination but the former symptom may be suppressed independently of the latter.     

In vitro germination and viability of buckwheat (Fagopyrum esculentum Moench) pollen

An in vitro method for the germination of common buckwheat pollen was developed. Pollen grains were successfully germinated in an artificial medium consisting of 0.2 g each of MnSO₄, Ca(NO₃)2.4H₂O and KNO₃, 0.04 g H₃BO₃, 15 g sucrose and 30 g polyethylene glycol (molecular weight approximately 20,000) dissolved in 100 ml of double distilled water. The viability of pollen was assessed by in vivo and in vitro germination tests at 20 °C and 25 °C over a 38 h time period. Pollen grains were collected and germinated at 4 h intervals from freshly harvested flowers grown under 16 h day length and a constant temperature. Maximum pollen viability was found 2 h and 6 h after first light when plants were maintained at 25 °C and 20 °C, respectively. Viability, as measured by germination percentage, was similar at both temperature regimes. Some pollen remained viable for approximately 34 to 38 h in intact flowers, but all pollen lost viability in less than an hour when stored at room temperature without humidity control. This revised version was published online in July 2006 with corrections to the Cover Date.