Evaluation of maize genotypes for drought and heat tolerance

Phenotyping of maize for tolerance to climatic stresses:

At CRIDA, a set of 94 genotypes received from NBPGR, DMR and CYMMIT was assembled and used for field phenotyping for drought tolerance during kharif 2012. Among these, 35 promising genotypes based on yield and drought tolerance were subsequently evaluated in rabi 2012-13 as well. Genotypes were evaluated based on 31 morpho-physiological traits and inter-relationship between the traits related to drought tolerance with grain yield were assessed under water deficit stress. In both the seasons, a significant decline in relative water content, leaf water potential, solute potential, membrane stability index, stomatal conductance, transpiration, SPAD chlorophyll and an increase in proline accumulation and total soluble sugars content, malondialdehyde content, leaf temperature and canopy temperature were recorded during stress period. Genotypes R2HK1-766(0), RJR-363, R1HK1-164-7-4, Z59-17, Z40-183, Z49-65, NSJ-366, RJR-385 NSJ-245, Z101-15, RJR208 maintained turgor and exhibited osmotic adjustment.

A simple high-throughput method to determine whole plant transpiration efficiency in crop plants was developed. Considerable genetic variation between water transpired and transpiration efficiency was observed in 100 maize genotypes tested. Higher transpiration efficiency was found to be associated with higher biomass production in maize.

Early ground cover was assessed using non-destructive phenotyping techniques standardized in the previous season which revealed a positive association with yield along with other traits such as relative water content and transpiration. Twenty crosses involving 5 tolerant [R1HKI-164D4, R2HKI-766(0), R1HKI-L-287, SNJ-2011-26 and RJR-363] and 4 susceptible genotypes [R1HKI-161, Z60-87, Z40-19 and Z93-194] were carried out with an aim to eventually identify QTLs for drought tolerance.

Two hundred SSR markers from NEARBY BINs associated to drought linked BINs have been selected from different bin location of 10 entire maize chromosomes to identify polymorphic markers. Out of 200 markers, 113 have been validated among 35 maize genotypes to get genotype specific amplification/primers. Out of 113 markers validated, 71 are polymorphic with two to six alleles per locus. Markers dupSSR21 and pumc1596 produced heterozygous type bands in genotypes SNJ-2011-26, Z32-87, Z40-183, RJR-198 and SNJ2011-26. Markers nc132 and pumc1185 produced unique band for genotypes R2HK1-766 (0), HK1-164-D4, RaHK1-L-287 and R1LM6, making it useful for QTL mapping and marker assisted introgression studies in these
genotypes.

Thirty two maize genotypes were sown in field on 30th January and 28th February during 2012, so as to coincide heat stress period with tasseling, anthesis, silking and grain filling stages. Various phenophases for the crop sown on II date of sowing were hastened mainly because of prevalence of relatively high temperatures during crop growth period. Temperature tolerant genotypes possessed low ASI values while the susceptible ones had higher ASI values. The contents of ascorbate and malondialdehyde (MDA), phenols, free amino acids declined while glucose, fructose and starch increased in the high temperature susceptible group as compared to the tolerant genotypes. Activities of superoxide dismutase, peroxidase and catalase were relatively lower while important sucrose metabolizing enzyme sucrose phosphate synthase was higher in the susceptible group. It was observed that traits like anthesis to silking interval (ASI), Cellular Membrane Stability Index (CMSI), canopy temperature, chlorophyll content and chlorophyll fluoresence were observed to be very vital for the selection of heat tolerance in maize.

Three maize genotypes DHM-117 (Hybrid), Varun (Synthetic) and Harsha (Composite) were assessed for their response to ambient (380 ppm) and elevated (550 ppm) CO2 levels in Open Top Chambers with regard to phenology, biomass accumulation, seed yield and HI. The phenology was early by 1.5 to 2 days under elevated CO2 in all the three maize genotypes; however the ASI was not influenced by elevated CO2 in DHMPolymorphic banding pattern of 35 maize genotypes with drought tolerance associated SSR marker – bnlg1016 423rd proof 13-62013 117 and Varun, whereas it was reduced by two days in Harsha. Biomass, seed yield and HI were all improved in all the 3 genotypes, although the response in harvest index was more in enhanced in Harsha.

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