Chikkappa G. Karjagi

Differential effect of immature embryo's age and genotypes on embryogenic type II callus production and whole plant regeneration in tropical maize inbred lines (Zea mays L.)

The study was undertaken to elucidate the effect of genotypes and age of immature embryo on callus induction, embryogenic type II calli production and regeneration from immature maize embryos. The immature embryos were excised from a selfed ear of ten elite Indian maize inbred lines on 6, 12 and 18 days after pollination. The mean callus induction, embryogenic type II calli production, and regeneration was highest across all the genotypes in 12 days old immature embryos and were 44.25, 26.12, and 11.20 per cent respectively. The significant differences were observed with respect to callus induction, embryogenic type II calli production and regeneration capacity between genotypes. The highest regeneration capacity was observed by immature embryo at 12 days after pollination (DAP) of genotype HKI1105 and CM300.

Impact of harvesting time on field carry over infestation of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in different maize genotypes

Study was carried out to evaluate the effect of time of harvest on field carry over infestation of rice weevil Sitophilus oryzae L. in maize. The maize ears were harvested at three different stages namely early harvest- i.e. just before physiological maturity (stage 1), timely harvest i.e. at physiological maturity (stage 2) and late harvest i.e. around ten days after physiological maturity (stage 3). The harvested maize ears were dried, shelled and stored separately over a period of 150 days. The emergence of F1 progeny of S. oryzae were significantly higher in late harvest maize (37.51) while relatively lower number in timely (27.09) harvest and lowest number in early harvest maize (14.47) were observed. The interaction effects between different stages of harvest × genotype, genotype × storage duration, different stages of harvest × storage duration, different stages of harvest × storage duration × genotype on F1 progeny emergence were found significant. Similarly, maize ears harvested at early and timely period, showed significantly lower weight losses as compared to late harvest maize. The mean per cent weight loss recorded at 90 and 150 days after storage were 0.66 and 2.24; 1.21 and 5.19; 2.24 and 6.33 in early, timely and delayed harvest maize kernels, respectively. The F1 progeny emergence was significantly and positively correlated with stage of harvest (r=0.4435). Also significant and positive correlations were found between weight loss and storage duration (r=0.3280). The kernel hardness was found significant negative correlation with progeny emergence and weight loss. The results indicated that physical and biochemical traits are also responsible for varying levels of resistance to S. oryzae. Use of cultural practices such as timely harvest of maize is one of the most promising approaches for efficient in minimization of field carry- over infestation of S. oryzae.

Breeding for Resistance to Insect Pests in Maize

The production of maize is constrained by various biotic stresses particularly insect pests. Infestation of insect pests on standing crop and stored grains not only reduces yield but also affects the quality of grains. The strategy for enhancing host plant resistance (HPR) is one of the cheapest, safe and sustainable methods for managing insect pests. Being a leading contributor to the world cereal basket, maize suffers from various insect pests. Maize has undergone various improvements through diverse breeding tools starting from selection to the present transgenic approaches to minimize the losses due to insect pests. This chapter provides an overview on major insect pests of maize, their distribution across the globe, methods of screening germplasm for resistance to insect pests, identification of sources of resistance, mechanisms of insect resistance, genetic nature of resistance and application of novel breeding methods for development of insect-resistant cultivars of maize.