ROOT-KNOT NEMATODES, Meloidogyne incognita (KOFOID AND WHITE, 1919) CHITWOOD, 1949 AND Meloidogyne javanica ( TREUB, 1885 ) CHITWOOD, 1949 INFECTING COTTON
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Date
1993
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AAU, Anand
Abstract
The experiments on root-knot nematodes(M. incognita and M. javanica) affecting cotton were conducted to study (i) effect of different inoculum levels of M, incognita and M, javanica on growth and development of cotton cv. Hybrid 8, (ii) effect of nematode infection on meteorological parameters, (iii) biochemical changes induced by nematode infection in cotton, (iv) histopathology of nematode infected cotton roots, (v) effect of interaction between M. incognita and M. javanica individually with Rotylenchulus reniformis and (vi) -screening of cotton varieties/lines to locate source(s) of resistance to M. incognita and M. javanica during 1991-92. The salient findings are : 1. An inoculum level of 100 M. incognita or M. javanica J2/plant and above was detrimental to the growth and development of cotton cv. Hybrid 8. Root, soil and total nematode population build up/plant significantly increased progressively with an increase in inoculum levels from 10 to 10,000 J2/plant. Reproduction rate of M. incognita or M. javanica decreased with an increase in inoculvmi levels. It was maximum 194.6 and 160,8 in the level of 10 J2 plant and minimxim 2.9 and 2.7 in 10,000 J2/plant for M. incognita and M. javanica, respectively, 2. The infection of M, incognita and M, javanica caused significant increase in leaf temperature and diffusion resistance with significant decrease in relative humidity and transpiration rate witli an increase in nematode inoculum levels in cotton cv. Hybrid 8. 3. Studies on biochemical changes induced by nematode feeding on cotton roots indicated that roots inoculated with 5,000 and 10,000 M. incognita J2/plant had signifificantly less peroxidase and polyphenoloxidase activities by 84.03 and 56.67 % ; 84.81 and 56.67 %, with higher total phenol content by 98.23 and 140.'26 %, respectively as compared to control. There were 86.55 and 88.65 % ; 50.00 and 60.00 % decrease In peroxidase and polyphenoloxidase activities and 73.89 and 92.92 % increase in total phenol contents in level of 5,000 and 10,000 M. javanica J2/plant, respectively as compared to control. 4. Histopathological studies revealed that after invasion second stage larvae of M. incognita and M. javanica penetrated the epidermal cells and migrated both inter and intracellularly and anchored to the vascular tissues. Giant cells consisted of uneven thickened, unbroken walls, dense cytoplasms and clusters of nuclei. Cells surrounding the nematode feeding site got darkened as compared to healthy roots. All stages of nematodes were found inside the root tissues feeding on vascular region. 5. Experiments on effects of interaction of M. incognita or M. javanica with R. reniformis revealed that plant height and fresh shoot weight were significantly reduced in case of plants inoculated with either M. incognita or M. javanica @ 2,000 J2/plant alone followed by Mi/Mj-Rr and Mi/Mj + Rr treatments. Control (uninoculated) plants gave significantly more plant height as compared to other treatments. The treatment of Rr - Mi/Mj, Mi/Mj-Rr and Rr alone did not differ significantly for plant height and fresh shoot weight. Fresh root weight was more in Mi/Mj alone and Mi/Mj - Rr inoculated plants. With regards to RKI , it was significantly more in Mi/Mj alone followed by Mi/Mj-Rr, Mi/Mj + Rr and Rr-Mi/Mj. Treatment of Mi/Mj alone and with or preceding Rr had maximum numbers of females, eggs, soil and total nematode population build up/plant over other treatments. Likewise Rr alone and Rr - Mi/Mj inoculated.plants had more numbers of Rr than Mi/kj + Rr or Mi/Mj - Rr treatments. 6. Screening of fifteen cotton varieties against M. incognita and M. javanjca separately indicated that none of the varieties/lines was either highly resistant or resistant to M. incognita or M. javanica. Five varieties viz., G 27, 949, G. Cot 10, V 797 and Varalaxmi were moderately susceptible, another five varieties viz., Digvijay, G. Cot.11,100; Hybrid 4 and Sanjay were susceptible and remaining three varieties viz., G. Cot 15, Hybrid 6 and Surat dwarf were highly susceptible types. Variety G 67 had susceptible and moderately susceptible and G, Cot 14 had highly susceptible and susceptible reactions to M. incognita and M. javanica, respectively.
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Plant Nematology, Agriculture, A Study