PHYSIOLOGICAL STUDIES ON SOME ELICITORS IMPROVING SOYBEAN TOLERANCE TO COTTON LEAF WORM

Abstract

This investigation was carried out to study the variation between six soybean genotypes (Giza 21, Giza 22, Giza 82, Giza 83, Giza 35 and Giza 111) in the resistance and susceptibility to infestation with cotton leaf worm. Also, effect of elicitors (methyl jasmonate and sodium nitroprusside) on increasing the susceptible genotypes to resist the infestation was studied. Each genotype was divided into three groups first group was treated with water, second group was foliar sprayed with methyl jasmonate (MeJA) and third group was foliar sprayed with sodium nitroprusside (SNP). Morphological and physiological studies were carried out on plant shoots and seeds.

The main experimental results can be summarized in the following:

1- Results showed a great variation among genotypes in resistance to cotton leaf worm infestation. Giza 111 and Giza 35 were found to be resistant genotypes. Giza 83 and Giza 21 were moderate resistant while Giza 22 and Giza 82 were found to be susceptible genotypes. On the other hand, treatments with MeJA or SNP enhanced the ability of susceptible genotypes to resist infestation with cotton leaf worm. Methyl jasmonate treatment was found to be more effective than sodium nitroprusside treatment.

2- Treatment with MeJA or SNP induced an increment in morphological criteria in soybean genotypes (shoot length, number of branches, number of leaves, assimilating area, fresh and dry weight of shoot, number of legumes in each plant, number of seeds in each legume, fresh and dry weight of legume and weight of 100 seed) comparing with the untreated plants.

3- Cotton leaf worm infestation induced a decrease in photosynthetic pigments content (Chlorophyll a, b and carotenoids) while, both treatments (MeJA and SNP) induced significant increases in pigment contents. Also, results showed significant increases in total soluble protein, total soluble sugars, proline, amino acid contents in shoots of treated groups with MeJA and SNP comparing with the untreated groups.

4- Lipid peroxidation and H2O2 contents showed a decrease in plants treated with MeJA and SNP under natural infection with cotton leaf worm comparing with untreated plants. On the other hand, an increment in secondary metabolites (phenols, flavonoids and tannins) contents was recorded in treated plants with MeJA and SNP.

5- Enzymatic and non enzymatic antioxidants were studied and showed significant increases in plants treated with MeJA and SNP comparing with the untreated plants under natural infection with cotton leaf worm.

6- Cell wall components showed an increment in total lipids, glycolipids and phospholipids contents in response to MeJA and SNP treatments while the same contents were decreased in untreated plants.

7- Fatty acids contents were studied in harvested seeds of soybean plants and showed a great differences as MeJA and SNP treatments was found to induce an enhancement in C18:2 and C 18:3 fatty acids content and a decrease in C 16:0 and C 16:1 contents comparing with seeds of untreated plants.

8- Retro markers results showed that soybean genotypes differ genetically and succeded in fingerprinting each genotype with specific bands except Giza 22. While it was not enough to predict molecular markers related to tolerance/ susceptibility in soybean.