Studies on resistance factors of maize plant against maize spotted stem borer, Chilo Partellus (Swinhoe)
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Date
2020
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DRPCAU, Pusa
Abstract
An experiment has been conducted during the year 2018 and 2019, in the cropping season of Kharif with twenty-five maize genotypes viz., Shaktiman-1, Shaktiman-2, Shaktiman-3, Shaktiman-4, Shaktiman-5, Devaki, Laxmi, Suwan, RHM-1, RHM-2, RHM-3, Deep Jwala, P-3535, P-3533, P-3550, P-3555, Dekalb-9188, Dekalb-9170, New Cross 76×11, New Cross 72×70, New Cross 73×11, New Cross 73×74, New Cross 52×65, New Cross 53×52 and New Cross 50×58 to assess their physical, biochemicals and molecular characteristic and find correlation between infestation levels and different traits under these observations. The physical characters included stem height, stem thickness, number of nodes, inter-node length, number of leaves, leaf length, leaf width, number of trichomes, trichome lengths and leaf angle between stem and leaf. Biochemical analyses included analysis of nitrogen, phosphorus, potassium, protein and chlorophyll including chlorophyll a, chlorophyll b and total chlorophyll while molecular analysis deled with real time analysis of closeness of different genotypes among each other in the term of morphological and biochemical traits. The crop sown in the Kharif in RBD design with 4 replications and for the infestation, artificial infestation has been done at the rate of 5 neonate larvae per plant on ten randomly selected plants in each replication. The data for physical characteristics was recorded at two different stages namely after 40 days of sowing and just before the tasseling stage, for biochemicals, the data was recorded of 40 days old plant while for SSR analysis, the genotypes were sown in pots separately. For the rating of infestation, leaf injury score method was adopted and infestation symptoms were rated in the scale of 1 to 9. The measurement of physical traits like stem height, leaf length and width, internode lengths were measured with the help of measuring scale while trichome density was counted with help of magnifying ocular. The data of stem thickness was recorded with help of slide caliper while the data of trichome length was recorded with help of binocular. The data of biochemicals like Nitrogen and protein have been recorded with kjel-dal and Winkelman’s formulae. Potassium was recorded with help of flame photometer while chlorophyll and phosphorus were recorded with the help of spectrophotometer. The molecular data was done with extraction of DNA and SSR analysis to obtain molecular level of diversity in the term of closeness of different genotypes. The infestation data was recorded after 20 days of artificial infestation and data leaf injury score was recorded. Total infestation per cent data was recorded on the bases of different larval injury and its immature stages presence and also other indices like excreta, pupal cases, exit holes, tunneling length were recorded after tasseling stage by splitting the stem of all maize genotypes.
Recorded traits, i.e., morphological traits like height of plant, stem thickness, number of nodes, inter-node length, number of leaves, leaves length and width, trichome density and length of trichomes and biochemicals like nitrogen, phosphorus, potassium, protein and chlorophyll (chlorophylls a, b and total chlorophyll) influenced by several interdependent environmental fluctuations leading to an difference in tracking of these traits. But these characteristics were found to be closely associated in related genotypes.
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There are several traits that have been identified as contributing in resistance against Chilo partellus in maize plants and a correlation between these traits and infestation have been developed to understand the quantitative relationship in different levels of pest infestation in different genotypes. In case of plant height, it was negatively significantly affecting. As per the results, it was recorded that genotypes having maximum height, were found to be less infested with the Chilo partellus. Stem diameter showed a positive but non-significant effect on infestation of maize spotted stem borer. It was observed that thicker stem supports more feeding of Chilo partellus but there is no such observation to establish a significant correlation between stem thickness and infestation. Number of nodes and inter-node length showed a negative and positive correlation respectively but non-significant association between infestation and number of nodes. Number of leaves, leaf length and leaf width are basically characterization of leaf and important in infestation due to they used as egg laying and initial feeding substrate and ultimately providing support to move towards to whorl and for further feeding. These characteristics were found to be non-significant positively correlated with infestation. It was observed that broad leaf genotypes were more susceptible in compare to narrow leaf genotypes. In case of maize, non-glandular type of trichomes are found and distributed on both leaf surfaces and stem while on lower surface very less numbers of trichomes are found in a few genotypes. They can inhibit infestation in many ways including the inhibition of egg laying and movement of neonate towards the leaf whorl. There are significant negative association between trichome density and infestation, while in case of trichome length, a positive significant association has been found. Leaf angle was measured between the stem and leaf and it was observed that plants with minimum leaf angles, found to be having greater infestation. A negative and significant correlation has been observed between leaf angle and infestation of Chilo partellus. Nitrogen and protein were recorded to be positively correlated with the infestation of maize spotted stem borer, Chilo partellus up to a significant level as it was observed that genotypes having maximum amount of nitrogen and protein showed more infestation. Nitrogen is a basic and major nutrient, required for vegetative growth and it make plants more valuable for insects more development. Many earlier workers have reported same association between nitrogen, protein and infestation. Phosphorus found in minor amount and showed a positive correlation with infestation but not up to the significant level. Potassium is very important in case of inducing resistance in plants. It was observed that genotypes having greater amount of potassium, showed less infestation of maize spotted stem borer, Chilo partellus. The association between infestation and potassium was recorded as negative and significant. Many earlier workers have reported same association between potassium and infestation. Chlorophyll a, chlorophyll b and total chlorophyll reported to be having positive correlation with infestation and chlorophyll a and total chlorophyll were found positive significant while total chlorophyll content showed non-significant association with infestation.