Jc Sekhar

Analyses of genetic diversity among maize inbred lines differing for resistance to pink borer and post-flowering stalk rot

Identification of the diverse sources of resistance is an important issue among the breeders for developing pest and disease free hybrids, to reduce the inoculum load, to prolong the life of inbred lines/hybrids and to reduce the cost of cultivation. Molecular diversity analysis was carried out among 23 maize inbred lines with respect to post flowering stalk rot and pink borer. Forty six SSR markers were employed among eight post flowering stalk rot (PFSR) and seven pink borer resistant lines along with eight other inbred lines to identify diverse resistant sources for developing resistant heterotic combinations to above pests and diseases. Number of alleles per SSR marker ranged from 2 to 9 averaging 4.11. The polymorphism information content (PIC) ranged from 0.272 to 0.839 with an average of 0.568. Discrimination rate (DR) of the markers ranged from 0.095 to 0.861 with a mean of 0.618. Number of alleles was highly correlated with PIC and DR. The pair-wise genetic dissimilarity values ranged from 0.05 to 0.84 with an overall mean of 0.64. Un-weighted neighbour joining clustering put 23 genotypes in two main clusters, which were further subdivided into 5 and 6 sub-clusters, respectively. We obtained 56 rare and 26 unique alleles in specific inbred lines, which can be used for identification of these lines. The present study has revealed considerable diversity among inbred lines differing for resistance against PFSR and pink borer; and provided ample scope for selection of parents for utilization in heterosis breeding

Potentiality of botanical agents for the management of post harvest insects of maize: a review

Natural products derived from plants are emerging as potent biorational alternatives to synthetic insecticides for the integrated management of post harvest insects of maize. In this paper, effectiveness of botanicals including plant extracts, essential oils, their isolated pure compounds, plant based nano formulations and their mode of action against storage insects have been reviewed with special reference to maize. Plant based insecticides found to be the most promising means of controlling storage insects of maize in an eco friendly and sustainable manner. This article also throws light on the commercialization of botanicals, their limitations, challenges and future trends of storage insect management.

Selection indices to identify maize (Zea mays L.) hybrids adapted under drought-stress and drought-free conditions in a tropical climate

Abstract. Drought stress is the most important production constraint in maize (Zea mays L.), especially in rainfed agriculture. To improve productivity of rainfed maize, the development of hybrids with tolerance to drought stress is an important objective in maize breeding programs. The present study was undertaken to identify maize hybrids that perform better under drought-stress and drought-free conditions by using various selection indices. These selection indices were calculated on the basis of yield (t ha–1) performance of hybrids measured under drought stress and optimum environments. A set of 38 cultivars was evaluated at 10 environments (representing five each of drought stress and optimum growing conditions). The average reduction in grain yield due to drought stress was 52%. Effects of genotype, environment and their interaction were significant sources of variation in determining grain yield, respectively explaining 5.0–7.4%, 55.0–60.2% and 12.0–15.0% of total variation in yield under drought-stress and drought-free conditions. Of eight selection indices considered for study, three indices such as harmonic mean, geometric mean, and stress tolerance index were identified as suitable for selection of genotypes capable of performing well both under drought-stress and drought-free environments. Drought response index and drought resistance index were found useful in identifying hybrids that performed better under drought stress. Stress susceptibility index was negatively correlated with yield measured under drought stress. Stress susceptibility index could be used as selection index but only in combination with yield performance data under water-deficit conditions in order to identify drought-tolerant hybrids with reasonable productivity. Test weight, shelling percentage, days to maturity, and ear girth were found to be useful traits for improving yield performance across diverse environments. Cultivation of identified drought-tolerant hybrids would be useful to enhance maize productivity in drought-stress environments.

Popping quality attributes of popcorn hybrids in relation to weevil (Sitophilus oryzae) infestation

A set of 21 popcorn hybrids were evaluated at multilocations to study the effects of weevil (Sitophilus oryzae) infestation on popping quality traits. Wide genetic variation for percent popping expansion (PPE) and grain popping percentage (GPP) after weevil infestation were observed. PPE and GPP varied from 6.09–85.21% and 4.33–66.67%, across locations, respectively. The mean PPE was 52.90%, while same for GPP was 23.46%. Significant effects of environment and genotype × environment interactions were observed for both PPE and GPP. Strong positive correlation (r=0.89) across locations was recorded between PPE and GPP. Despite weevil infestation, popcorn hybrids viz., PH114 (PPE: 83.18%, GPP: 54.11%), PH110 (PPE: 69.27%, GPP: 33.11%), PH103 (PPE: 65.84%, GPP: 26.78%), PH112 (PPE: 64.91%, GPP: 29.22%) and PH109 (PPE: 64.48%, GPP: 29.00%) were identified as promising with desirable popping quality traits. Many of the popcorn hybrids possessed undesirable popping characteristics (12 hybrids with <60% PPE; 18 hybrids with <30% GPP) upon infestation. Despite having a common notion that popcorn genotypes are relatively resistant than other types of maize grain, many of the popcorn hybrids were highly susceptible to weevils leading to undesirable popping quality attributes. The study emphasizes the need for breeding weevil resistant popcorn genotypes possessing desirable popping quality attributes.

Genetics of resistance to stored grain weevil (Sitophilus oryzae L.) in maize

Abstract Stored grain weevil (Sitophilus oryzae) has emerged as important storage grain pest of maize, causing substantial economic losses. Owing to high costs and environmental hazards of pesticides, host plant resistance holds promise for effective control of weevils. In the present study, a set of experimental maize hybrids generated using line × tester mating design were evaluated against S. oryzae. Significant variation for grain weight loss (GWL) (6.0–49.1%), number of insect progeny emerged (NIP) (17.8–203.3), grain hardness (GH) (263.1–495.4 N), and pericarp thickness (PT) (60.3–161.0 μm) was observed. Strong positive association was observed between GWL and NIP. GH and PT did not show any correlation with GWL and NIP. Additive and non-additive gene actions were important for both GWL and NIP. Promising inbreds and experimental crosses identified can be effectively utilized in the resistance breeding programme. In majority of promising crosses having desirable SCA effects, one of the parents had desirable GCA effects, indicating that selection of inbred parents based on per se performance for generating resistant crosses may be possible. The commercial hybrid checks were highly susceptible compared to experimental hybrids. The inbreds and experimental hybrids identified hold promise in developing weevil resistant maize cultivars offering sustainable solution to management of weevils in maize.

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.

Mass Production of Biocontrol Agents of Insect Pests

With the increased need and awareness of integrated pest management concept among the farmers, there is increased emphasis on the utilization of biocontrol agents for the management of pests. Though their demand is increasing, yet their availability is far from sufficient. The biocontrol agents, particularly parasitoids and predators, have short life span and they cannot be stored for long. Their transportation also requires certain specific conditions which are difficult and expensive. These are some of the important reasons that private sectors are not much interested in them. Of late, there have been quite a few inventions for the automation in the mass production of biocontrol agents which have removed bottlenecks for their economic and efficient production and have facilitated the mass production of biocontrol agents. Now, the biocontrol agents can be mass produced at a small scale/cottage industries just on the lines of sericulture or apiculture. Simple, low cost and down to earth technology can be used for their mass production. They can be marketed in the region where they are produced. The simple methods suitable for their transportation have been developed. The production of biological control in cottage industries is also likely to increase their acceptabilities in the rural areas.

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.

Analyzing the role of sowing and harvest time as factors for selecting super sweet (−sh2sh2) corn hybrids

Providing suitable environment for high-kernel sweetness and yield is important for successful commercialization of sweet corn hybrids. Twenty five super sweet corn genotypes were evaluated at three-sowing and -harvest dates. Genotype, sowing- and harvest- time had significant influence on kernel sweetness accounting 33.8%, 9.1% and 3.9% of total variation, respectively. Genotype × sowing time, genotype × harvest time and genotype × sowing time × harvest time interactions contributed 13.8%, 8.2% and 18.9% of total variation, respectively. Kernel brix across genotypes ranged from 16.1–25.5%. Sixty eight per cent of the hybrids attained highest brix in third sowing compared to 12% and 16% in first and second sowing, respectively. Sixty four per cent of the genotypes attained peak in brix at 24-DAP (days after pollination), while 24% and 12% genotypes had highest brix at 20-DAP and 28-DAP, respectively. Genotypes with stable brix across sowingand harvest-time have been identified. Sowing time also had significant influence on anthesis, cob- and fodderyield. Late sowing favoured kernel sweetness and cob yield. Cob- and fodder- yield possessed positive correlation, but did not show any association with kernel sweetness. The information generated here holds immense significance in the genetic improvement of sweet corn.

Resistance to the spotted stem borer Chilo partellus (Swinhoe) and pink stem borer Sesamia inferens walker in maize

Two hundred twelve maize inbred lines were screened against Chilo partellus (Swinhoe) and Sesamia inferens Walker during rainy and post rainy seasons, 2012, respectively, under artificial infestation in field conditions. Based on the leaf injury rating (LIR) scale (1–9), 110 inbred lines with LIR < 3.0 along with resistant and susceptible check were re-screened against C. partellus during rainy season 2013 in augmented design under artificial infestation. Of the 212 inbred lines, 34 genotypes with LIR < 3.0 were re-screened along with three checks in replicated randomized block design during post rainy season 2013, against S. inferens under artificial infestation. The six genotypes viz., PFSRS2, AEBYC5341-1, P390AM/CMLC4F230-B-2, AEBCYC534-3-1, CML384X176F3- 100-9 and P63C2-BBB-17B were found to be the least susceptible to C. partellus, and 29 genotypes were categorized as moderately susceptible. Of the 34 inbred lines screened against S. inferens, six inbred lines namely WNZPBTL 9 (3.2), WNZPBTL 8 (3.5), CML 338 (3.6), WNZ EXOTIC POOL DC2 (3.1), CML 424 (3.2), WNZPBTL 91 (3.4) recorded LIR less than resistant check CM 500 (3.8) and 15 inbred lines were considered as moderately susceptible. These maize inbred lines could be utilized as sources of resistance against C. partellus and S. inferens.