Satish Lodha

Soil solarization, summer irrigation and amendments for the control of Fusarium oxysporum f. sp. Cumini and Macrophomina phaseolina in arid soils

Abstract Field tests were carried out to examine the efficacy of soil solarization in conjunction with amendments (urea at 20 Kg N ha −1 and farmyard manure) for the control of wilt ( Fusarium oxysporum f. sp. cumini ) of cumin ( Cuminum cyminum ) and dry root rot ( Macrophomina phaseolina ) of clusterbean ( Cyamopsis tetragonoloba ). During the summer of 1987, solarization of soil by covering it with transparent polyethylene sheets for 15 days greatly reduced the population of the two soilborne pathogens at 0–30 cm depth. As a result, significant reductions in the incidence of wilt, dry root rot and weed populations, and improvements in seed yields were recorded in solarized plots. Soil amendments extended the effectiveness of solarization by restricting the rebound of Fusarium , even after two successive crops of cumin, compared to solar heating alone. Similarly Macrophomina populations did not increase significantly after one crop of clusterbean. Populations of these pathogens were also reduced considerably merely by the natural heating of the moistened bare soil after amendments. These results suggest a new approach to disease control by the application of summer irrigation in hot arid regions.

Inactivation of Macrophomina phaseolina Propagules during Composting and Effect of Composts on Dry Root Rot Severity and on Seed Yield of Clusterbean

Survival of a heat-tolerant pathogen Macrophomina phaseolina, causing dry root rot of clusterbean, was studied by incorporation and retrieval of infected residue samples at various stages of the composting process of pearl millet (Pennisetum glaucum) and clusterbean (Cyamopsis tetragonoloba) residues. During the heating phase, temperatures varied from 48–51°C at 30cm and 60–62°C at 60cm depth in compost pits. Reduction in survival of M. phaseolina propagules (13–23%) was significantly higher in the residues enriched with 4% urea-N and kept at 60cm compared to 2% urea-N and at 30cm. However, a heat phase (48–62°C) was not enough to completely eradicate M. phaseolina propagules from infected residues. Further reductions (54–61%) in survived propagules were achieved by sub-lethal temperatures (48–53°C) when moistened compost materials were exposed to heat during summer days. Beneficial effects of composts were ascertained on dry root rot intensity, seed yield of clusterbean and densities of M. phaseolina,Nitrosomonas and antagonists in soil. In a two-year field study, all the composts significantly reduced plant mortality due to dry root rot and increased the yield of clusterbean. The highest disease suppression and yield promotion were recorded in soil amended with pearl millet compost and cauliflower leaf residue compost, respectively. Soil amendment with compost also lead to a significant reduced density of M. phaseolina and an increased density of antagonistic actinomycetes, lytic bacteria and Nitrosomonas. Among composts, greater potential of cauliflower compost in enhancing population of antagonists in soil was discernible.

Population changes of Macrophomina phaseolina and Fusarium oxysporum f. sp. cumini in oil-cake and crop residue-amended sandy soils

Abstract Population changes of Macrophomina phaseolina and Fusarium oxysporum f. sp. cumini were followed in a sandy soil amended with mustard and castor cakes or nitrogen-enriched pearl millet residue, singly or in combined form. Populations of both the pathogens were reduced by 100% in the mustard-cake-amended soil within a period of 30 days after addition. Amendment with nitrogen-enriched pearl millet residue significantly reduced the population of M. phaseolina within 45 days, but not that of F. oxysporum. However, incorporation of pearl millet residue in both types of cakes delayed the rate of reduction. The induced suppressiveness in the cake-amended soil was associated with a substantial increase in the population of antagonistic actinomycetes. These results suggest that amendment of soil with mustard cake in fields infested with M. phaseolina and F. oxysporum f. sp.cumini may reduce yield loss caused by dry root rot of guar (Cyannopsis tetragonoloba (L.) Taub.) and wilt of cumin (Cuminum cyminum L.).

Factors influencing population dynamics of Macrophomina phaseolina in arid soils

The quantitative determination of Macrophomina phaseolina population in an arid soil was carried out utilizing a selective medium. The population of the fungus increased under continuous monocropping with a susceptible host, but considerable reduction was recorded with crop rotation or a change in crop sequence. The effects of fungi, bacteria, actinomycetes, total microbial population, minimum and maximum soil temperature on the survival of M. phaseolina population were studied in the absence of a crop at different soil depths. Highest population and survival rates were recorded at 0–5 cm soil depth. Correlation and path coefficient analyses were carried out to determine the role of individual factors influencing M. phaseolina population. In winter months, low temperature and high actinomycete population were found to be the major factors governing the reduction of the population of M. phaseolina.

Integrating sub-lethal heating with Brassica amendments and summer irrigation for control of Macrophomina phaseolina

Effects of varying intensities of sub-lethal heating were ascertained in improving the efficiency of Brassica amendments and summer irrigation on survival of Macrophomina phaseolina, a dry root rot pathogen. Sub-lethal heating (45–55 °C) of M. phaseolina infested dry soil reduced the viable propagules by only 12.8% in a period of 90 days. One summer irrigation without sub-lethal heating caused 33.9% reduction in M. phaseolinapropagules, which improved to 43.3% when it was combined with 60 days of sub-lethal heating. Addition of the Brassicaamendments to irrigated soil resulted in significant reduction (60.4–71.6%) in counts of M. phaseolinabut this reduction improved (89.4–96.1%) when sub-lethal heating was combined with amendments. Mustard oil-cake (0.18% w/w) was found to be the most effective with reduction but a 94% inoculum reduction by mustard pod straw (0.36% w/w) was also achieved at 0–30 cm soil depth under similar conditions. Moderate heat level could not exert detectable weakening effect on M. phaseolinapropagules. These results suggest a practical cultural control of soil-borne pathogens by combining sub-lethal heating, Brassica amendments with one summer irrigation.

Biological Control of "Fusarium oxysporum" f.sp. "cumini" with "Aspergillus versicolor"

A native heat-tolerant strain of Aspergillus versicolor (Vuill.) Tirab. highly antagonistic to Fusarium oxysporum f. sp. cumini (Foc) was isolated from arid soils. In tests performed to ascertain its antagonistic activity against Foc as compared to Trichoderma harzianum, a 99.2 and 96.4% reduction in Foc propagules was achieved in A. versicolor and T. harzianum infested soil respectively. The reduction of Foc propagules in Foc and A. versicolorinfested soil was also determined. In a liquid-culture test, even at a low concentration of 0.5 ml cell-free filtrate, A. versicolor inhibited mycelial growth of Foc. Population changes of A. versicolor were examined at different soil moisture gradients, where maximum survival and multiplication of A. versicolor was estimated at 50% of moisture holding capacity. In general, with increasing concentrations of A. versicolor inoculum, soil population densities of Foc went down. Studies on thermal resistance showed that A. versicolor survived and multiplied even at 65°C. Soil amended with A. versicolor alone, or with a combination of T. harzianum and Verbisina enceloides residues was significantly better at reducing Foc than was non-amended control soil. A marked increase in the root length of cumin was observed in soil amended with A. versicolor or T. harzianum or both. The results suggest that A. versicolor has a potential value for use against Fusarium in hot arid soils because it can survive under dry and high-temperature conditions.

Infection and colonization of jojoba byGanoderma lucidum

In arid conditions in India,Ganoderma lucidum (Leyss: Fr.) P. Karsten was found to cause root rot diseases in jojoba (Simmondsia chinensis (Link) Schneider) plants. In the rainy season, 10–15-year-old jojoba plants growing in the proximity of aGanoderma-infectedAcacia tortilis tree, developed disease symptoms. Twigs of affected plants started drying from the top of the branch; leaves turned yellowish brown and finally abscissed; plants dried up within 1 to 3 months. Basidiocarps developed from decaying roots near the collar region and produced colored stalks and fruiting caps. Pathogenicity of the fungus was established by keeping the infected root segments in direct contact with roots of healthy jojoba plants. Root rot symptoms were expressed within 5 months in inoculated plants subjected to moisture stress.

Suppression of Soilborne Plant Pathogens by Cruciferous Residues

Soilborne plant pathogens case heavy losses in many agriculturally important crops. The inoculum density of soilborne plant pathogens increases with increased years of cultivation of susceptible crops, and the inoculum density is directly proportional to the disease intensity in the field. In severe cases, total devastation forces aggrieved farmers to either abandon the land or shift to less susceptible but often less profitable crops. Therefore, effective control measures need to be developed that are economically, environmentally and technologically effective and acceptable. At present growers in many developing countries are dependent on cultural control measures for the partial reduction of soilborne plant pathogens. Among management strategies, use of organic amendments as crop residues, composts or manures has been found to be of wider acceptance and practical relevance in most of the agricultural production systems. The incorporation of plant residues in soil as green manure or at the end of crop growth has been a common practice for years. Higher plants contain and release an enormous variety of biologically active compounds, some of which have been exploited as potential pesticides. Use of cruciferous residues or making crucifers as a part of rotation will not only provide reasonable control of these pathogens but may also improve population of antagonists in soil, which will induce soil suppressiveness.

Influence of soil solarization on the viability of Fusarium solani in an arid environment

Abstract Efficacy of soil solarization (polyethylene mulching) was tested against a root rot fungus, Fusarium solani, in hot arid environment. Mulching during the month of June increased soil temperatures by as much as 12 and 9°C at 5 cm depth in dry and wet plots, respectively, resulting in a pronounced reduction of F. solani population. An initial population of 250 propagules g‐1 soil was reduced to 13 (dry) and 7 (wet) propagules during a period of 15 days. Elimination of propagules at 15 and 30 cm soil depth was relatively low. Considerable reduction in the Fusarium population occurred in moistened nonmulched soil, indicating a possibility of disease control by the application of a single irrigation in summer months.