D S Cheema

Hybrid Tomato Breeding

Summary Tomato is one of the most popular vegetable crops grown across the world. Its genetics is much studied among vegetable crops, resulted in the reorganization of its commercial exploitation of hybrid vigor since last hundred years. Tomato has tremendous potential of heterosis for earliness, total yield, resistance attributes and uniformity. Hybrid tomato varieties will continue to predominate high input agricultural systems and may expand under some lower input systems where benefits can be demonstrated. Increasing demand for hybrid seeds can stress commercial hybrid seed production abilities. At present most of the hybrid seeds of tomato is being produced by hand emasculation and hand pollination. The advances in genetic emasculation methods can prove very useful for making the hybrid seed production profitable and ensure the supply of hybrid seed at cheaper rates to the growers.

Utilization of rin, nor, and alc Alleles to Extend Tomato Fruit Availability

ABSTRACT In some locations, fruit of tomato (Lycopersicon esculentum Mill.) is only available for short times. Excess production of tomato during these short periods leads to a saturated market and low prices. These periods can be followed by scarcity and high prices. A few mutant genes, i.e., alcobaca (alc), ripening inhibitor (rin), and non-ripening (nor), in heterozygous form, extend shelf-life and take more time to go from mature green to red ripe as compared to normal genotypes. The present study was conducted on 79 genotypes of tomato (15 normal genotypes, 4 mutant homozygotes, and their 60 F1 hybrids produced in line × tester fashion) in two seasons to determine whether these mutant alleles can extend the fruit availability period of tomato by storing fruit longer on the plant and then at room temperature or in controlled conditions. The F1 hybrids involving these mutant alleles delay fruit ripening on the plant, improve yield potential, increase shelf-life, and extend fruit availability. A few hybrids are recommended for further testing in the main season. No hybrid was found suitable for production in periods of high temperature due to their low yield potential, which likely meant that parental lines lacked heat tolerance. Incorporation of these mutant alleles in heat-tolerant genotypes and developing hybrids by crossing them with normal or heat-tolerant lines could be a viable method to further extend fruit availability period of tomato.

Seeds of Tomato (Solanum lycopersicum L.) Hybrids Incorporating rin, nor, or alc Alleles Exhibit Heterosis for Yield and Quality Traits

The high price of hybrid seed of tomato (Solanum lycopersicum L.) may be compensated for by realized higher profits obtained from cultivation of hybrids. The objective of the present study was to ascertain the magnitude and direction of relative heterosis in hybrids involving rin, nor, or alc alleles for yield and quality traits, as well as the existence of correlation among relative heterosis for these traits. Significant relative heterosis was observed for all the traits. Not even a single hybrid exhibited significant and negative relative heterosis for marketable yield and number of fruits per plant. The magnitude of relative heterosis varied from −37.06% to 45.72% for average fruit weight, −13.68% to 11.36% for pH, and −53.73% to 54.62% for ascorbic acid. The F1 hybrids of tomato had, in general, higher marketable yield and number of fruits per plant as compared with their mid-parental values. However, the average weight, pH, and ascorbic acid of fruits of tomato hybrids were higher, lower, or equal to their mid-parental values. The increase in yield of most of the hybrids was accompanied by an increase in fruit number, fruit weight and ascorbic acid but was not correlated with increase or decrease in pH. Fruit number played greater role than fruit weight in improving marketable yield of tomato hybrids. Future studies on tomato may be aimed to validate the existence of a correlation among an increase in ascorbic acid of hybrids with a simultaneous increase in their marketable yield, fruit number and fruit weight.

Genotype × Environment Interactions for Shelf Life and Yield Attributes in Tomato Hybrids Heterozygous at rin, nor, or alc Loci

ABSTRACT Development of high-yielding cultivars with better shelf life and consistent performance across seasons is one of the important objectives of tomato (Lycopersicon esculentum Miller) breeding programs. Heterozygous individuals, i.e., F1 hybrids, are reported to be more stable to environmental variation than homozygous ones due to their ability to perform better under stress conditions. The present study was conducted to identify F1 hybrids heterozygous at rin, nor, or alc loci having wider adaptability across main and late planting conditions, besides possessing higher yield and better shelf life than check hybrids. The variation among environments was linear. All hybrids showed genotype×environment interactions for all traits. Shelf life of different hybrids significantly fluctuated from their respective linear response to environments and was non-predictable, while yield attributes (total yield/plant and number of fruits/plant) did not fluctuate and were predictable. Most of the tomato hybrids heterozygous at rin, nor, or alc loci showed above average stability for shelf life and yield attributes. However, 19 hybrids showed below average stability for total yield/plant and were suitable for main season planting only. The most stable hybrid was Spectrum × alc-IIHR-2050 having high-mean yield (1.25 kg/plant), nearing unity regression coefficient (0.91) and nonsignificant deviation from regression (-0.11). It possessed higher yield and better shelf life index (9.31) than check hybrids viz., TH-1 (0.92 kg/ plant, 5.49) and Naveen (0.84 kg/plant, 6.01) and is recommended for multilocation trials across the state for cultivation in main and late planting conditions.

Combining Ability and Heterosis for Quality and Processing Traits in Chili Pepper (Capsicum annuum L.) Involving Male Sterile Lines

Non-availability of genetic male sterility (GMS) in genetically diverse genotypes and the problem of rouging fertile plants in hybrid plot necessitated the development and testing of new F1 hybrids of chili pepper (Capsicum annuum L.) using cytoplasmic-genetic male sterility (CGMS) system and identifying good combiner inbred lines for transferring male sterility system in to them. Twelve inbred lines including a CGMS and a GMS line were crossed in a half-diallel fashion following Griffing’s method II and model 1 (fixed effect). All 78 genotypes were evaluated for eight quality traits for two consecutive years at Ludhiana, India. Pooled analysis revealed that variances for parent × year were non-significant for all traits except capsaicin in oleoresin and coloring matter in oleoresin, whereas variances attributable to hybrid × year and parent vs. hybrid × year were significant for all traits except dry matter content and oleoresin content. Both GCA × Y and SCA × Y interactions were significant for all traits except dry matter content. The GMS line was a good combiner for six traits and the CGMS line for only one trait. Better parent heterosis of high magnitude was detected for powder yield (275%) and oleoresin yield (309%). The hybrids having high powder yield coupled with high dry matter content and those having low pungency in oleoresin were identified. We recommend that male sterility system be transferred into a few good combiner lines for cost-effective hybrid seed production and for broadening the genetic base of male sterile lines.