Yonatan Elkind

Variation in the response of melon genotypes to sudden wilt

SummaryDifferences in the response of melon genotypes to the sudden wilt disease were observed in several field trials conducted during 1993–1994 in the Arava region of southern Israel. Generally, the disease was more severe in the late summer growing season which is shorter and has higher temperatures than the spring and autumn growing seasons. The Oriental pickling melon breeding line P6a was the most tolerant among the entries tested. The response to the disease was also studied using two segregating families and their progenitors. BSK (tolerant) × P202 (susceptible) and P6a (tolerant) × D17 (susceptible). Wilting percentages of F1, F2 and backcross families were intermediate between the parents, suggesting an additive mode of gene action.

Influence of different concentrations of 1-methylcyclopropene and times of exposure on the quality of 'Galia'-type melon harvested at different stages of maturity

Summary This study evaluated the influence of different 1-methylcyclopropene (1-MCP) concentrations (150, 300 or 450 nl l–1) applied for 6, 12 or 24 h at 20°C on ‘Galia’ type melon (Cucumis melo L., reticulatus cv. ‘Trooper’), harvested at three stages of maturity, based on epidermal colour: green (~ 116 h° [Hue angle]); green/yellow (~ 105 h°) or yellow (~ 90 h°), and stored for 15 d at 5°C then 3 d at 20°C. The optimal treatment with 1-MCP to suppress ripening of fruit harvested at the green/yellow stage of maturity was 300 nl l–1 for 24 h at 20°C, as evaluated by delayed colour development, retention of firmness, and low weight loss. This treatment also significantly reduced chilling injury (CI) and the development of decay, compared with non-treated fruit, or fruit treated with 150 nl l–1 1-MCP. However, 1-MCP did not suppress senescence in fruit harvested at the yellow stage of maturity, as evaluated by external and internal quality parameters. 1-MCP did not affect total soluble solids contents. When fruit was harvested at the green stage, 450 nl l–1 1-MCP reduced the rate of post-harvest ripening significantly, resulting in fruit of unacceptable colour development and firmness. 1-MCP delayed by 8 – 9 d the onset of the climacteric peak of CO2 production and ethylene evolution in fruit harvested at the green/yellow stage of maturity. The quantities of CO2 and ethylene production in 1-MCP-treated fruit were lower than those in controls.

Quantitative analysis of the transgene variability among primary tobacco transformants

The aim of this study was to develop a model for the quantitative estimation of the genetic and environmental variance components in the first generation (T1) of transgenic plants, in which the transgene effect is considered as a source of genetic variation. The experimental population consisted of T1 independent transgenic plants (ITPs). Forty-two ITPs of tobacco were generated, containing a chimaeric gene comprising the cauliflower mosaic virus (CaMV) 35S promoter and the reporter gene β-glucuronidase (GUS). From each ITP, four cuttings were grown in a randomized block design, and GUS activity in the leaves was determined. The mean GUS activity of the ITPs ranged from 0.55 to 167.9 pmol MU per mg protein per min. Testing of the statistical assumptions of the model revealed a significant ‘scale effect’, resulting from correlation between the intra-ITP variance and the average GUS activity of the ITPs. Log GUS activity (LGA) and power of −0.15 of GUS activity (TGA) scale transformations eliminated the scale effect. For GUS activity, the inter-ITP variance was only 28% of the total variance in the experiment, whereas for LGA and TGA it was 72% and 76%, respectively. The opposite was true for the intra-ITP variance, which was reduced from 58% to 18% and 16%, respectively. The experimental design allowed partitioning of the phenotypic variance in T1 transgenic plants into genetic and environmental components. According to the original scale GUS activity, most of the phenotypic variance was due to environmental variance; the common tendency to interpret this variance as an outcome of position effect and other genetic changes due to transformation leads to incorrect findings. In the present example, after scale transformation the genetic component was 80% of the phenotypic variance.

Effects of the ms10 gene, polygenes and their interaction on pistil and anther-cone lengths in tomato flowers

Pistil and anther-cone lengths (PL and AL) are important traits in tomato hybrid seed production with the use of male-sterile flowers and in fruit production of fertile plants under high temperature. The effects of the male sterility gene ms10, polygenes, and their interaction on tomato PL and AL and on the difference between them (DIF) were studied in two experimental populations, each obtained from a different cross and comprised of F3 families derived from selfed heterozygous (Ms10/ms10) F2 plants. Data were analysed using a mixed model for a single gene, polygenes, and their interaction. The presence of the ms10 gene resulted in AL and PL that were shorter by 2.5 (±0.1) mm and 1.2 (±0.1) mm, respectively, in male-sterile flowers than in male-fertile ones. Thus DIF was greater by 1.3 (± 0.1) mm in male-sterile flowers than in male-fertile flowers. ‘Main polygenic variance’ was found in all three traits. The variance due to interaction between polygenes and the ms10 gene, even when significant, was always smaller than the variance due to polygenes alone, or to environment. Emasculation of the ms10 male-sterile parent appears to be unavoidable for the efficient production of hybrid seeds.

A mixed model for the effects of single gene, polygenes and their interaction on quantitative traits. 2. The effects of the nor gene and polygenes on tomato fruit softness.

The effects of the nor gene, polygenes and their interaction on tomato fruit softness one (SF1) and nine (SF9) days after picking at “breaker” stage of ripening were studied using two experimental populations, each obtained from a different cross and comprised of F3 families derived from selfed heterozygous (nor/+) F2 plants. The results were analysed using a mixed model for a single gene, polygenes and their interaction. A multiplicative nor × polygenes interaction was detected for SF1, and it was included in the model by log transformation. The multiplicative coefficients of the nor effect on family means were 0·76, 1·07, 1·23, and 0·77, 1·06, 1·22 for nor/nor, nor/+, +/+, respectively, in population 1 and 2, each. “Net Polygenic Heritability” was estimated as 0·51 and 0·27 in two different populations. The corresponding multiplicative coefficients for SF9 were 0·62, 1·06 and 1·51 and 0·60, 1·07 and 1·56. After log transformation, a random nor × polygenes interaction was also found for SF9. It was concluded that a rather small experiment of the design used (13–21 families, 305–461 individuals) facilitated simultaneous detection of the effects of a single gene, polygenes and their interaction on quantitative traits, as well as characterization of the nature of the interaction. This provided better understanding of the genetic control, as well as improved estimates of genetic parameters than those obtained when lack of such interaction was assumed.

Sensory evaluation of ‘Galia’-type melons treated with 1-methylcyclopropene after prolonged storage

Summary Exposure to 300 nl l–1 1-methylcyclopropene (1-MCP) suppresses internal and external ripening parameters in melons harvested at the green/yellow stage of maturity. We investigated the sensory attributes and volatiles of ‘Galia’-type melons treated with the ethylene activity inhibitor 1-MCP at the green/yellow stage of ripening, compared to untreated and commercially-treated fruit after prolonged storage. Organoleptic and volatile analyses were performed after 15 d storage at 5°C and a 3 d marketing simulation at 20°C. 1-MCP-treated fruit had a lower level of total volatiles (3,334 µg kg–1 FW) compared to untreated fruit, or to fruit washed and waxed according to commercial practice. Most of the volatiles were esters, while a few were aldehydes, or ethanol. Methyl acetate, as well as methyl 2-methylbutanoate, which are associated with the ‘fruity’ aroma note, were significantly higher in 1-MCP-treated fruit. The “green” note, due to hexanal, remained relatively high in 1-MCP-treated fruit after storage, while it was not detected in commercially-treated fruit. Ethanol, ethyl acetate, and ethyl hexanoate volatiles that are associated with “off-flavour” and over-ripening were significantly higher in commercially-treated fruit. A trained panel described the sensory properties of the three treatments. The overall aroma notes were significantly more intense in commercially-treated fruit, while in 1-MCP-treated fruit they were much less evident. 1-MCP-treated fruit had the strongest “green” note, while commercially-treated fruit had the weakest. A very strong ‘acetone’ note was detected after commercial treatment, and was associated with ‘unpleasant’ and ‘non-typical’ notes. Members of an untrained panel preferred 1-MCP-treated melon and disliked commercially-washed and waxed fruit.

Genotype by environment interaction of tomato blossom-end scar size

SummaryLarge blossom-end scar is a disorder in tomato fruit which reduces its marketability. The disorder is affected by genotype and by several environmental factors and therefore the genotype by environment interaction was studied by stability analysis. Blossom-end scar size was recorded for 4 tomato cultivars grown in 6 fields. The blossom-end scar size (BSC) was affected by the genotype, the field and their interaction. Stability analysis revealed that most of the interaction resulted from different stability of the cultivars. Heterogeneity of the slopes was significant (P<0.0013). The stability slopes were 0.29, 0.74, 1.11 and 1.85 for BR-214, FA-38, Hayslip and Suncoast, respectively. The stability slopes seemed to associate with the means of the cultivars over all environments, which were 1.57, 2.92, 3.84 and 5.43, respectively. Analysis of a blossom-end scar index (BSI), which also takes fruit size into account, revealed stability similar to BSC. It was concluded, that selection for small BSC under most conditions would yield cultivars with small and stable BSC under most growing environments, however differences between genotypes in non-inducing environments are expected to be small.

Honeybee Pollination Affects Fruit Characteristics of Sweet Pepper Grown Under Net-Houses

Abstract In modern agriculture, many high-value cash crops that were formerly cultivated in open fields are now grown in greenhouses and net-houses. While changing the cultivation environment, attention is needed to ensure adequate pollen transfer to the stigma due to absence of wind, isolation from wild pollinators and low viability of reproductive organs due to the extreme temperature under those conditions. This study explores the effects of honeybee (Apis mellifera L.) pollination on various fruit characteristics of several different cultivars of sweet pepper (Capsicum annuum L.) under enclosed conditions. In all 16 cultivars examined during two growing seasons, bee pollination increased numbers of seeds per fruit, and had a significantly positive effect on fruit placenta weight, fruit weight, fruit width and fruit-wall thickness. While fruit diameter consistently correlated with bee pollination, fruit-length response alternated between seasons. It may be concluded that although bee pollination is a powerful tool for affecting fruit characteristics in sweet pepper, each cultivar exhibits different levels of response. Cultivars need to be evaluated separately, relative to market demand, when considering the use of bees for pollination.

Diallel analysis over two environments for blossom-end scar size in tomato

SummaryTo investigate genetic regulation of blossom-end scar size in tomato (Lycopersicon esculentum Mill.), a half diallel cross including 10 parents was grown under warm fall conditions in Bradenton, Florida, and cool winter conditions in Hazeva, Israel. The parents were a random sample representing all available fresh market tomato breeding lines commercially grown under subtropical field conditions. A randomized, complete block design with three replications was used and the blossom-end scar index (BSI), a measure for scar size relative to truit size, was measured on 40 and 25 fruits per plot in Bradenton and Hazeva, respectively. Analysis of variance for BSI indicated highly significant (P=0.001) variation among parents and among F1s in both environments. In Bradenton and Hazeva both, the difference in average BSI between parents and F1s was not significant suggesting insignificant overall dominance effects. Further partitioning of variation within F1s indicated that general combining ability (GCA) effects were highly significant in both environments, whereas specific combining ability (SCA) effects were significant at P=0.001 in Bradenton, but only at P=0.05 in Hazeva. Estimated variance components for GCA and SCA effects indicated that BSI inherited mainly additively in both environments. Analysis combined over environments indicated that variation in sensitivity to environments was 5-fold higher among parents than among F1s. The genotype x environment variance component was not large enough to justify testing over more than one environment for population improvement purposes and early testing of hybrids. Evaluation of inbred lines, however, may have to be done in more than one environment, especially for ‘Suncoast’-derived material. Under temperatures in Hazeva, genotype differences were more pronounced and heritabilities higher than under high temperatures in Bradenton. The estimated overall single plot heritability was 0.63. Breeding lines with a pointed blossom-end morphology (e.g. NC 8276 and NC 140 in this study) generally had small blossom-end scars, and intercrossing of these lines or crossing with non-pointed, moderately smooth breeding lines generally resulted in smooth hybrids.