Anand Agricultural University, Anand

The experiments on reniform nematode, Rotylenchulus reniformis, in bidi tobacco conducted to study the life cycle, effect of temperature and pH on hatching of eggs, nematode survival and virulence/ histopathology, effect of nematode on seed germination and seedling development, inoculum potential in relation to growth of tobacco seedlings and reaction of tobacco.varieties to nematode revealed that R. reniformis completed its life cycle from egg to egg in 27 to 32 days at 30 to 32°C on bidi tobacco variety Anand 119, The fecundity of nematode was on an average 83 eggs per egg mass and reproduction was amphimitic. Among the different temperatures (5 to 45°C with an increment of 5°C) studied, egg hatching of nematode was significantly more a t 30°C as compared to the rest, while per cent nematode survival was significantly-more at 15°C than at the remaining temperatures. But the nematode virulence on castor variety Anand 6-4 was significantly more when incubated at 5°C as compared to the remaining temperatures. As regards the different pH levels (2 to 10 with an increment of one), nematode egg hatching was significantly more at 7 pH than the remaining levels. The nematode survival was significantly more at 9 pH than the rest, while nematode virulence on castor variety Anand 6-4 was significantly more at 9 pH than the rest barring 8 pH. Histopathological studies indicated that young female penetrated the epidermal and cortical parenchyma tissues and reached the endodermal layers intracellularly through parenchyma. The orie third anterior portion of the female remained embedded in the root. Several cells of pericycle layer surrounding the head of the nematode formed giant cells. R. reniformis reduced 36,36, 57.56, 7.91, 64.32 and 23.91 per cent reduction in seed germination, green and oven dry seedlings weights as well as number of transplantable and total seedlings over sterilized soil. The nematode also retarded the nutrients uptake by tobacco seedlings to the tune of 9.83 (Nitrogen) ,1.75 (phosphorus), 5.93 (Potassium), 10.70 (Calcium) and 1-8.59 (Magnesium) per cent under infected soil. The nema population increased from the initial level of 250 to 1400 per 100 g of soil in 45 days. Among different levels of inoculum (o, 10, loo, 1,000 and 10,000 nematodes per pot), the inoculum level of 100 nematodes per pot and above reduced the green shoot weight and plant height of tobacco seedlings. The level of 10,000 nematodes per pot while being at par with the level of 1,000 nematodes per pot had significant depressing effect on green root and green as well as dry shoot weights of tobacco seedlings as compared to the rest barring the level of 100 nematodes per pot. The level of 10,000 nematodes per pot reduced significantly less plant height as compared to the rest. The soil population per pot and total number of nematodes per plant increased significantly upto 1000 nematodes per pot, thereafter, the population did not increase significantly in the level of 10,000 nematodes per pot. similarly the reproduction of R. reniformis increased with an increase in nema population upto 3,000 nematodes per pot (0 to 5.14), It was low (0.69) in the level of 10,000 nematodes per pot. Likewise nutrients uptake also decreased with an increase in nema population and inverse correlationship observed between inoculum levels and nutrients uptake was very high with the variation in coefficient from -0.865 to -0.706. Ihe reaction of tobacco varieties viz. Anand 2, Anand 119, Dharmaj Kaliu (DK), S 20, GT 4, K 49, K 20 and Kumkumathri (Bidi types), Anand 145, and 47-75 (Chewing types) and CTRI Special, 16-103 and VaSCR (VFC types) to R. reniformis revealed none to be free from R. reniformis infestation. Varieties GT 4, Anand 145 and Anand 2 were less preferred hosts while VaSCR was highly preferred by R. reniformis. The rest of the varieties were intermediate.

In a split plot designed experiment carried out during the years 1977-78 and 1978-79 the three treatment levels (damage thresholds) of 10, 15 and 20 percent bollworm damage to fruiting bodies of selected size-group (from full grown squares to young bolls) were evaluated on calendar-based and need-based schedules for their effects on yield, number of undamaged bolls, bollworm damage to retained bolls and loculi, shedding of fruiting bodies, and earliness in maturity. The applications of carbaryl 0.25 percent + DDT 0.25 percent mixture at 10 and 15 percent treatment levels were found to be equally effective in giving a maximum yield of (good seed cotton) when they were continued on need basis (Average 3506 and 3117 kg/ha at 10 and 15 percent levels respectively) and weekly basis (Average 3852 and 3409 kg/ha at 10 and 15 percent levels respectively). Amongst three frequencies of application under fixed schedules, the weekly-based frequency of application was the best.

Anand Agricultural University, Anand

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