M.I.S. Gill

Genotype identification and inference of genetic relatedness among different purpose grape varieties and rootstocks using microsatellite markers

Twenty-seven (27) grape genotypes representing different grape groups namely table, wine, juice grapes and rootstocks with present or potential future importance for sub-tropical viticulture were characterized with 29 microsatellite markers spanning over 15 linkage groups of ‘Syrah’ x ‘Grenache’ linkage map. The objective of the investigation was to establish the unique molecular identity of the promising genotypes and to know the diversity status among them. The study revealed that most of the markers were highly informative and polymorphism information content (PIC) of 21 out of total 29 markers was ≥ 0.8. The use of two simple sequence repeat (SSR) markers was sufficient enough to resolve the differences among all the grape genotypes. The unweighted Neighbour-Joining tree generated using DARwin 5.0 software classified the germplasm into three different clusters. The grouping of the different genotypes in the tree had distinct order. Genotypes derived from the same species were in one group, while the genotypes having both or one parents common in their pedigree formed separate group. Likewise, the rootstocks were clearly differentiated from grape varieties. However, the varieties could not be differentiated into table, juice and wine types. The findings of the study will be helpful in authentication of the genotypes and their use in the future grape breeding programmes. Keywords : Vitis species, table, juice, wine varieties, rootstocks, DNA fingerprinting, diversity analysis African Journal of Biotechnology Vol. 12(2), pp. 134-141

Somatic Embryogenesis, In Vitro Selection and Plantlet Regeneration for Citrus Improvement

Citrus is the most widely cultivated fruit crop across the globe. The commercially cultivated varieties and rootstocks are the adapted genotypes and need improvement for one or few traits. Such targeted improvement though the conventional breeding approaches is hindered by the complex biological attributes of Citrus such as polyembryony and sterility and sometimes sexual incompatibility with the donor sources. The cell- and tissue culture-based techniques such as somatic embryogenesis and in vitro selection are vital for the improvement of Citrus. The somatic embryogenesis facilitates improvement of Citrus through somatic hybridization and genetic transformation. Somatic hybridization has been used for the genetic improvement of both scion and rootstocks. Somatic hybridization-mediated scion improvement involves production of superior allotetraploids that can be used for crossing with diploid elite varieties to develop seedless triploids. The development of cybrids by combining cytoplasmic genome from Satsuma mandarin and nuclear genome from desired varieties is also an attractive approach. In the rootstock improvement, somatic hybridization targets packaging of resistance to different biotic and abiotic stresses in a single rootstock. The allotetraploid somatic hybrids reduce tree size and can improve adaptability of the composite trees by imparting resistance to different stresses. The in vitro selection has been used for improvement against biotic (mal secco, Phytophthora-induced diseases and canker) and abiotic stresses (salt, cold and Al toxicity) in Citrus. Techniques like shoot-tip grafting have shown promise for restoring the true yield potential of citrus cultivars by cleansing them from infectious virus and virus-like diseases.

Breeding Avenues in Fruit Crops for Imparting Resistance Against Insect Pests

Insect pests cause huge losses to crops directly or indirectly, and fruit crops are not an exception to this statement. The application of insecticides for minimizing qualitative and quantitative losses in fruit crops is not only hazardous to consumers but also results in undesirable environmental and ecological consequences. The development of insect-resistant fruit varieties is an ecofriendly alternative to chemical control and is a durable solution to the menace of insect pests. The host plant resistance against insect pests is based on certain structural and biochemical features of the plants. The transfer of traits to the elite germplasm through conventional breeding is often limited by the long pre-bearing juvenile phase of the fruit crops. The genomics-assisted breeding, which is the integration of genomic tools with conventional breeding, can prove helpful in overcoming these shortcomings. Among the genomics approaches, biparental mapping, association mapping and genomic selection have direct relevance in genetic improvement of fruit crops. The biparental mapping helps in locating the gene/QTLs for insect pest resistance. Through this approach, the host plant resistance against leaf miner in citrus, woolly apple aphid and rust mite in apple, gall mite in black currant and aphid in raspberry has been mapped. Similarly, the use of genetic engineering-based approaches like transgenesis, cisgenesis, RNAi and other potential techniques, which could enhance the fruit crop resistance against insect pests, has been discussed in this chapter.