Jagadeesh Patil

Effect of nitrogen supply form on the invasion of rice roots by the root-knot nematode, Meloidogyne graminicola

Rice is capable of taking up both nitrate (NO3 −) and ammonical (NH4 +) forms of nitrogen (N). It is largely grown under flooded cultivation when NH4 + is the main form of available soil N. The root knot nematode, Meloidogyne graminicola, can cause serious damage to rice crops and disturb N uptake and translocation. We have investigated if the N supply form can influence the susceptibility of rice to this important pest. Roots supplied with a 100-fold lower supply of calcium nitrate (0.1 mM Ca(NO3)2) showed a higher level of nematode infection as measured by the gall index. Plants supplied with 2.85 mM of Ca(NO3)2 were more infected compared with the same dose of ammonium nitrate (NH4NO3) or ammonium chloride (NH4Cl). 15NO3 − influx studies showed significantly smaller uptake of nitrate in nematode-infected roots when compared with non-infected control plants. The electrophysiological studies showed that resting cell membrane potentials of nematode-infected plants were significantly smaller (less negative) than those of non-infected control rice. Furthermore, when the cellular responses to NO3 − were compared, these also showed significantly smaller nitrate transport activity in nematode-infected roots (4.7 ± 1.2 mV) when compared with non-infected control plants (11.9 ± 3.4 mV). Taken together, the 15NO3 − influx and electrophysiological measurements clearly showed that the root NO3 − transport activity was severely decreased in nematode-infected roots. The results also show that regulation of NO3 − concentration at critical periods of nematode infection of rice root can provide a non-nematicidal method of nematode management.

Synergism of Entomopathogenic Nematode and Imidacloprid: A Curative Tool to Coconut white Grub, Leucopholis coniophora (Coloeptera: Melolonthinae)

Insecticide imidacloprid and entomopathogenic nematode (EPN), Heterorhabditis indica alone and in combinations of imidacloprid and EPN were evaluated against early and late 3rd instars of coconut white grub, Leucopholis 3rd coniophora. Field collected instars white grubs were placed in pots with sweet potato treated with imidacloprid, the EPN, or both. In all nematode-imidacloprid combinations, both early and late 3rd instars grub mortality was significantly higher than in the H. indica alone and imidacloprid alone treatments. Combinations of imidacloprid and nematodes had a strong synergistic effect on mortality at different concentrations of imidacloprid. Nematodes were admixed with various concentrations of imidacloprid ranging from 0.04 to 1.25% could not significantly affect the survival of infective juveniles resulting in only a negligible mortality (3.5%). Results revealed that different imidacloprid concentrations, exposure time and interaction between imidacloprid and exposure time not affected nematodes mortality in bioassay. Combinations of imidacloprid and entomopathogenic nematodes may provide a powerful and economically feasible curative control in white grub management in coconut.

The effect of root-knot nematode, Meloidogyne graminicola, on the quality and vigour of rice seed

The root-knot nematode, Meloidogyne graminicola, is a serious pest of rice known to reduce grain yield. The effects of a series of infestation levels of M. graminicola on the nutritional and seed quality parameters of the grain have been studied under pot and field conditions using two cultivars of rice, a basmati, cv. Pusa Sugandh-5 and a non-basmati, cv. Pusa-44. The 1000 grain weight was significantly reduced by as much as 44.5% in cv. Pusa Sugandh-5 and 50.7% in cv. Pusa-44 seed when the parent plants were grown in soil with very high levels of M. graminicola infestation. The protein and amylose contents of the grains were significantly reduced in both the rice cultivars. The seed germination percentages of both the rice cultivars were also reduced as the nematode inoculation rates increased from 1-8 second-stage juveniles (J2) cm−3 in a pot experiment. Similar trends were also observed in field conditions. There was a significant decrease in the seedling vigour indices of both the rice cultivars. These results showed that the rice grains produced on plants infected with the nematode M. graminicola were lighter in weight and had poorer nutrient qualities, such as amylose and protein content. Further, if these grains were used as seed, the germination percentage was lower and, even more importantly, seed vigour was poor compared to the seed obtained from plants grown in M. graminicola-free soil.

Effect of root nitrogen supply forms on attraction and repulsion of second-stage juveniles of Meloidogyne graminicola

Three experiments were conducted to compare the attraction and repulsion of second-stage juveniles (J2) of the root-knot nematode, Meloidogyne graminicola, to rice plants supplied with different forms of nitrogen. The rice plants were hydroponically grown in a full nutrient solution containing different concentrations (0.1 or 10.0 mM) of nitrate (NO3 −) or forms of nitrogen supply (2.85 mM calcium nitrate (Ca(NO3)2), ammonium nitrate (NH4NO3) or ammonium chloride (NH4Cl)) for 2 weeks. Five rice plants were placed with their roots in one corner of a Perspex X or Y-chamber partly filled with agar and J2 were inoculated onto the chambers. The data show that J2 of M. graminicola were significantly attracted towards the roots of rice plants grown in hydroponics containing 0.1 mM NO3 − and 2.85 mM Ca(NO3)2, but repelled by 10.0 mM NO3 −, 2.85 mM NH4NO3 and NH4Cl. The results suggest that the application of ammonia-based nitrogen fertiliser to the rice nursery bed may interfere with nematode attraction and thus reduce invasion, and the application of chemical nitrification inhibitors to rice nursery beds may decrease nematode invasion.

Entomopathogenic nematodes: a potential biocontrol agent against eggplant ash weevil Myllocerus subfasciatus Guerin (Coleoptera: Curculionidae)

Eggplant ash weevil, Myllocerus subfasciatus , is an important pest of eggplant that attacks other solanaceous crops in Asia and Southeast Asia. The potential efficacy of two species of entomopathogenic nematodes (EPN), Steinernema carpocapsae and Heterorhabditis indica , against third instar and pre-pupal stages of this pest was tested under laboratory and poly-greenhouse conditions. In this present study, both stages were susceptible to EPN species but the pre-pupal stage was more susceptible. Steinernema carpocapsae was the most effective species against pre-pupal stages. In a pot experiment, among the EPN species tested, S. carpocapsae caused significantly greater mortality (20-100%) than H. indica (16-92%) against pre-pupal stages and S. carpocapsae caused 16-92% mortality in third instar larvae, while H. indica caused (12-80%) mortality. Both EPN species were able to reproduce in third instar and pre-pupal stages of ash weevil, but progeny production rate for H. indica was significantly higher than those of S. carpocapsae . Our observations also revealed that efficacy of EPN against M. subfasciatus varies with developmental stages of M. subfasciatus and EPN species; therefore, no generalisation can be made. Our findings provide the first insight into the biocontrol potential of S. carpocapsae and H. indica against third instar and pre-pupal stages of M. subfasciatus .

Relationship between population density of root-knot nematode, Meloidogyne graminicola and the growth and nutrient uptake of rice plant

Root-knot nematodes cause hypertrophy and hyperplasia of the vascular and cortical root tissues that reduce the absorption and transport of nutrients and water from soil. Aboveground symptoms are mistaken as nutrient deficiencies. The farmers tend to apply higher doses of fertilizers than necessary for a nematode-free crop, that not only causes economic loss but also avoidable soil and groundwater pollution. The nitrogen (N), phosphorus (P), potassium (K), iron (Fe) and zinc (Zn) contents were determined in the rhizosphere soil and leaves of a non-basmati Pusa-44 and a basmati Pusa Sugandh-5 cultivars of rice grown in soil infested with varying levels of Meloidogyne graminicola under pot and field conditions. The N, P, K, Fe and Zn contents in the rice leaves were significantly reduced in both the rice cultivars infestated with M. graminicola under both pot and field conditions. The degree of reduction did not significantly differ in the two cultivars. Pusa Sugandh-5 had relatively greater biomass than Pusa-44, but both the cultivars appeared to be similarly susceptible to M. graminicola. The residual contents of N, P, K, Fe and Zn in soil were more with increasing nematode population. Thus, the nutrients remained unutilized in the soil while the plant suffered severe nutrient deficiencies and growth reduction in the presence of nematode infestation.