Studies on Character Improvement in Tomato (Solanum lycopersicum L.) by Heterosis

Most of the tomato varieties in Bangladesh are of inbred type and produced low yield indicating need to develop high yielding variety through the hybridization. Heterosis breeding is used to improve yield and quality of tomato because traditional methods cannot be used to achieve this goal. A half diallel design was employed to develop F1s from seven parents of winter tomato. 21 F1s along with their parents were evaluated for yield and quality traits. Heterosis analysis revealed that heterotic vigor was present for growth and yield characters among hybrids. Heterosis for better parent was negative for days to flowering, days to harvest, harvest duration, number of locules, and number of seeds per fruit but positive for fruit set, number of fruits per plant, yield per plant, pericarp thickness and TSS. None of the hybrid was heterotic for all characters simultaneously. The hybrids G5, G13, G16, G17, G18, and G20 had 25.73, 19.92, 39.20, 36.49, 53.77, and 50.31% higher heterosis compared to the better parent, respectively, for fruit yield per plant as well as for many other yield contributing traits. High heterosis for yield appears to be the consequence of heterosis of yield attributing traits; therefore, these hybrids offer scope of developing improved commercial lines through heterosis breeding.

Morphological, pedigree, and molecular distances and their association with hybrid wheat performance

The objectives of this work were to estimate the genetic distance among wheat genotypes using morphological, pedigree, molecular, and combined morphological and molecular measures, to determine the correlations between these measures, and to evaluate the combining ability of the genotypes. Three generations and two planting designs were studied. Six wheat genotypes were crossed using a diallel design. The F1, F2 and F3generations were evaluated in the field, in the crop seasons of 2003, 2004 and 2005, under spaced plant and full-row planting designs. The estimated general and specific combining abilities of tested hybrids were influenced both by the generation and the planting design. The correlation coefficients among the distance measures and between these measures and genotype performances of different generations for the two planting designs were low to moderate. In order to obtain a more precise estimate of the genetic distance among cultivars and its association with the hybrid performance, more than one generation, planting design, and genetic distance estimation technique should be employed.

Genetic analysis of plant height and diameter at ground level of silver birch (Betula platyphylla) seedlings

Six silver birch (Betula platyphylla) parents of diverse provenances were crossed according to Griffing 4 diallel design, and the plant height and diameter at ground level (DGL) of their F1 progeny were observed. The analysis of general combining ability (GCA) and specific combining ability (SCA) showed that two phenotypes were simultaneously controlled by additive and non-additive effects. The GCA between two phenotypes in a parent, and GCA of the same phenotype among different parents displayed significant differences: Q2 from Qingyuan was the best of the parents, followed by M2 from Maoer-mountain. On the other hand, the SCA of two phenotypes in a cross and the SCA of a phenotype among different crosses also varied considerably: the cross between E8 from Finland and Q1 from Qingyuan showed the highest SCA of plant height and DGL. The heritability of plant height and diameter at ground level was strong (over 60%), suggesting that these phenotypes can be used for early selection.

Heritability of Terbacil Herbicide Tolerance in Strawberry

A partial diallel design was used to investigate the inheritance of tolerance to terbacil herbicide in cultivated strawberry, Fragaria ×ananassa Duch. Two tolerant cultivars, `Honeoye' and `Earliglow', two moderately tolerant cultivars, `Lester' and `Allstar', and two susceptible cultivars, `Red Chief' and `Guardian' were used as parents to create populations that segregated for tolerance to the herbicide. Tolerance rankings of the populations closely coincided with expected rankings based on the published tolerance levels of parental cultivars. `Honeoye' and `Earliglow' derived populations had the highest average tolerance ratings, while `Guardian' derived populations had the lowest tolerance ratings. Heritability was estimated at h2 = 0.50, indicating that significant progress in increasing the tolerance of new cultivars to terbacil can be achieved through traditional recurrent selection procedures. General and specific combining abilities suggest that the tolerant cultivars in this study may be fixed in their tolerance and that increased mean tolerance will be most apparent in progenies combining tolerant and susceptible cultivars. As such, a broader pool of germplasm may be needed to develop cultivars that are more tolerant than those in this study. Chemical names: terbacil (3-tert-butyl-5-chloro-6-methyluracil)

Potential to increase yield in lucerne (Medicago sativa subsp. sativa) through introgression of Medicago sativa subsp. falcata into Australian adapted material

The effect of interspecific heterosis in crosses between Medicago sativa subsp. sativa and M. sativa subsp. falcata was assessed. Three sativa and 3 falcata plants were crossed in a diallel design. Progeny dry matter yield and natural plant height were assessed in a replicated field experiment at Gatton, Queensland. Yield data were analysed using the method of residual maximum likelihood (REML) and Griffing’s model 1. There were significant differences between the reciprocal, general combining ability (GCA), and specific combining ability (SCA) effects. As expected, S1 populations were lower yielding than their respective intraspecific cross and falcata × falcata crosses were significantly lower yielding than sativa × sativa crosses. Some of the interspecific crosses indicated substantial SCA effects, yielding at least as well as the best sativa × sativa crosses. We have demonstrated the potential usefulness of unselected M. sativa subsp. falcata as a heterotic group in the improvement of yield in northern Australian adapted lucerne material, and discuss how it could be incorporated into future breeding to overcome the yield stagnation currently being experienced in Australian programs.

Epistatic Interactions Between smell-impaired Loci in Drosophila melanogaster

Odor-guided behavior is a polygenic trait determined by the concerted expression of multiple loci. Previously, P-element mutagenesis was used to identify single P[lArB] insertions, in a common isogenic background, with homozygous effects on olfactory behavior. Here, we have crossed 12 lines with these smell impaired (smi) mutations in a half-diallel design (excluding homozygous parental genotypes and reciprocal crosses) to produce all possible 66 doubly heterozygous hybrids with P[lArB] insertions at two distinct locations. The olfactory behavior of the transheterozygous progeny was measured using an assay that quantified the avoidance response to the repellent odorant benzaldehyde. There was significant variation in general combining abilities of avoidance scores among the smi mutants, indicating variation in heterozygous effects. Further, there was significant variation among specific combining abilities of each cross, indicating dependencies of heterozygous effects on the smi locus genotypes, i.e., epistasis. Significant epistatic interactions were identified for nine transheterozygote genotypes, involving 10 of the 12 smi loci. Eight of these loci form an interacting ensemble of genes that modulate expression of the behavioral phenotype. These observations illustrate the power of quantitative genetic analyses to detect subtle phenotypic effects and point to an extensive network of epistatic interactions among genes in the olfactory subgenome.