Evaluation of Heat Stress Tolerance Indices in Maize Inbred Lines

The heat stress during flowering, pollination and grain filling stages affect the productivity of maize. Twenty maize inbred lines were evaluated in field and plastic houses using alpha lattice design with two replications during spring season of 2016 at National Maize Research Program, Rampur, Chitwan, Nepal. Five stress tolerance indices namely stress susceptibility index (SSI), stress tolerance index (STI), tolerance index (TOL), geometric mean productivity (GMP) and mean productivity (MP) were applied to identify superior heat stress tolerant lines. The results showed that STI, SSI, GMP and MP indices were the more accurate criteria for selection of heat tolerant and high yielding lines. The positive and significant correlation of GMP and MP with grain yield under both conditions revealed that these two indices were more applicable and efficient for selection of inbred lines. The biplot analysis identified the groups of tolerant and sensitive inbred lines. The maize inbred lines namely RL-140 and RML-91 found high yielding and low stress susceptibility in both conditions. These results suggest that the inbred lines namely RL-140 and RML-91 should be use a source of heat tolerance for maize breeding program

GENETIC DIVERSITY FOR HEAT TOLERANT RELATED TRAITS IN MAIZE INBRED LINES

The present investigation was carried out at research field of National Maize Research Program (NMRP), Rampur, Chitwan, Nepal during February to June 2016. The objective of this investigation was to estimate genetic variability and identify suitable maize inbred lines under heat stress condition. Twenty maize inbred lines were evaluated in alpha lattice design with two replications under normal and plastic house condition. Several secondary traits, namely yield attributes such as - ears per plant, cob length, cob diameter, number of kernels row-1, number of kernel rows cob-1, number of kernel ear-1, shelling percentage, thousand kernel weight and morpho physiological traits such as anthesis silking interval, plant height, ear height, silk receptivity, leaf senescence, tassel blast, leaf area index and leaf firing exhibited significant genotypic and phenotypic association with grain yield under heat stress. Maize inbred lines RL-140, RML-76, RML-91 and RML-40 were exhibited shorter anthesis silking interval, lowest value of tassel blast, leaf firing, and leaf area index with highest value of cob diameter and length, ear per plant, number of kernel row ear-1, number of kernel ear-1 and number of kernel row-1,shelling percentage, silk receptivity and grain yield in heat stress condition.High heritability along with genetic advance as well as significant positive correlation with grain yield recorded for traits grain yield with number of kernel ear-1, silk receptivity, shelling percentage, and thousand kernel weight indicates presence of additive gene effect early selection and could be used as target traits to improve maize grain yield under heat stress condition. But significant negative association grain yield as well as moderate heritability with low genetic advance for traits anthesis silking interval, tassel blast, leaf firing and leaf area index showed significant negative association with grain yield, and these traits could be improved through the use of hybridization and hybrid vigour.Therefore maize inbred lines RML-91, RL-140, RML-76 and RML-40 were can be used for development of hybrid for heat stress condition

Analysis of genetic diversity among the maize inbred lines (Zea mays L.) under heat stress condition

High temperature adversely affects the plant physiological processes: limits plant growth and reduction in grain yield. Heat stress is often encountered to spring sowing of maize in spring season. Twenty maize inbred lines were studied for days to 50 % anthesis and silking, anthesis–silking interval, leaf firing, tassel blast, SPAD reading and leaf senescence, plant and ear height, leaf area index, ear per plant, cob length and diameter, number of kernel/ear, number of kernel row/ear, number of kernel row, silk receptivity, shelling percentage, thousand kernel weight and grain yield in alpha lattice design at National Maize Research Program at Rampur, Chitwan,Nepal with the objective to identify superior heat stress tolerant lines. Analysis of variance showed significant difference for all the traits. Result of multivariable analysis revealed that twenty inbred lines formed four clusters. The resistance inbred lines and susceptible inbred lines formed different clusters. The members of cluster 4 were found to be tolerant to heat stress due to they had lowest value of tassel blast, leaf firing, and leaf area index with highest value of cob diameter and length, ear per plant, number of kernel row/ear, number of kernel/ear, number of kernel row, shelling percentage, silk receptivity and grain yield whereas as members of cluster 1were found most susceptible due to they had longer anthesis silking interval, with maximum tassel blast and leaf firing along with no grain yield under heat stress condition. From this study inbred lines RL-140, RML-76, RML-91 and RML-40 were found most tolerant to heat stress. These inbred lines belonging to superior cluster could be considered very useful in developing heat tolerant variety and other breeding activities