Eco-friendly approaches for the management of fenugreek root rot

To evolve eco-friendly management of fenugreek root rot caused by Rhizoctonia solani, a field trial was conducted during Kharif 2002 and Rabi seasons of 2002–2003 and 2003–2004. Experiments were conducted with eight treatments and three replications in RBD using the variety CO-2. The pooled analysis of the three season data showed that seed treatment with Trichoderma viride at 4g/kg of seed + soil application of Trichoderma viride at 5 kg/ha + soil application of neem cake at 150 kg/ha (T₃) recorded a percent disease index (PDI) of 23.1 versus 65.5 PDI in the control which accounted for a disease reduction of 64.7%. It was on par with seed treatment with Trichoderma viride at 4g/kg of seed + soil application of T. viride at 5 kg/ha (T₂) which reduced the disease incidence by 62.3% (24.7 PDI). The chemical treatment used for comparison, i.e. seed treatment with carbendazim + soil drenching at 0.1% + soil application of neem cake at 150 kg/ha recorded the lowest PDI of 16.8 with 74.4% disease reduction. Among the various treatments T₃ gave a seed yield of 572.7 kg/ha followed by T₂ (555.7 kg/ha). Treatment T₇ recorded the highest yield of 578.7 kg/ha. In the control plot the recorded yield was only 359.3 kg/ha. Though T₃ was more effective at reducing the disease incidence than T₂, the C:B ratio was higher (1:9.1) in respect of T₂ than T₃, which gave a C:B ratio of only 1:3.9. Hence, seed treatment with T. viride at 4g/kg + soil application of T. viride at 5kg/ha is a cost effective, eco-friendly management strategy for fenugreek root rot.     

Assessment of laboratory methods for evaluating cassava genotypes for resistance to root rot disease

Field evaluation of six cassava genotypes for resistance to root rot disease was compared with three rapid laboratory methods (whole root inoculation, root slice inoculation, and stem inoculation) for resistance screening. Both the field evaluation and the three laboratory methods separated the varieties into resistant and susceptible groups. Genotypes 30572 and 91/02324 were resistant while 92/0247, 92/0057 and TME-1 were susceptible. One genotype (30001) was not consistent in its reaction between field evaluation and laboratory assays. In the laboratory assays with three fungal pathogens, different pathogens varied in their levels of virulence on host genotypes. With the most virulent pathogen (Botryodiplodia theobromae), the majority of the genotypes reacted in the same way across trials with the root slice and whole root assays. Due to the good correlation between the whole root assay and the field results, we recommend this for the routine assessment of cassava resistance to root rot disease and for the analysis of virulence of pathogen isolates. However, because of the advantages in terms of economy of labour, space, time, quantity of root and inoculum required, the root slice assay could be used for the preliminary screening of large cassava accessions. The selected genotypes can then be further screened with the whole root inoculation method.     

Suppression of root rot of mung bean (Vigna radiata L.) by Streptomyces sp. is associated with induction of peroxidase and polyphenol oxidase

Five strains of Streptomyces sp. were evaluated in vitro for their ability of inhibiting the mycelial growth of Macrophomina phaseolina, the causal agent of root rot of mung bean (Vigna radiata L.). Among the Streptomyces sp. strains tested, PDK showed the maximum in vitro inhibition of mycelial growth of M. phaseolina and recorded an inhibition zone of 21?mm. The strains CBE, MDU, SA and ANR recorded inhibition zones of 18, 16, 13 and 11?mm, respectively. These Streptomyces sp. strains were tested for their growth-promoting efficiency on mung bean seedlings. Among them, CBE and PDK recorded the maximum increase in shoot length, root length and seedling vigour compared with control, followed by MDU. Three Streptomyces sp. strains (CBE, MDU and PDK) that showed higher levels of inhibition of growth of M. phaseolina in dual culture assay and plant growth-promoting activity were tested for their biocontrol activity against root rot under greenhouse and field conditions. Seed treatment or soil application with powder formulation of Streptomyces sp. strains CBE, MDU and PDK was effective in controlling root rot disease; but, combined application through seed and soil increased the efficacy in both the greenhouse and field trials. Among the treatments, seed treatment plus soil application with powder formulation of Streptomyces sp. strain CBE proved to be most effective, which reduced the root rot incidence from 26.8% (with non-bacterised seeds) to 4.0% in Trial I and from 32.0 to 4.9% in Trial II. The above treatment recorded the highest yield in both the field trials, and the yield increase was 78 and 74% over control in Trial I and Trial II, respectively. Isozyme analysis of the Streptomyces sp.-treated plants indicates that seed treatment plus soil application strongly induce the activities of peroxidase (PO-1 and PO-2) and polyphenol oxidase (PPO-2 and PPO-3) in mung bean. Among the three strains tested, Streptomyces sp. strain MDU- treated plants showed higher levels of activities of PO and PPO. Based on the above findings, it can be concluded that both the direct inhibition of pathogen and induced resistance might be involved in the control of root rot of mung bean by Streptomyces sp.     

Performances of improved cassava (Manihot esculenta Crantz) cultivars against root rot disease and yield in cassava-maize intercropping systems under natural infection

This study examined the performances of 21 cassava cultivars in two cropping seasons on the field against root rot disease and the yield in cassava-maize intercrop. Data were collected on number of root/plant, weight of root (t/ha) and disease severity (DS) on rotted roots at 12 and 16 months after planting (MAP), respectively. There were significant (P ≤ 0.05) differences for DS at 12 and 16 MAP in both seasons with cultivar TMS 97/JW2 having the least DS score. TMS 97/JW2 was resistant to the root rot pathogen, while eleven other cultivars were moderately resistant to the disease at 16 MAP. There was no consistency in the roots weight for the cultivars over the two cropping seasons but higher roots weight was recorded at 16 MAP than 12 MAP with different cultivars having highest roots weight at these periods. Intercropping maize with cassava does not have any management potential on root rot development.     

Effect of heterogeneous distribution of nutrients on root growth, ABA content and drought resistance of wheat plants

Heterogeneous distribution of nutrients influenced morphology of wheat roots; they were shorter and had more laterals at the site of high nutrient content. The roots outside the nutrient-rich patch were longer and penetrated deeper in the soil than those of the plants supplied with the same quantity of nutrients but having them homogeneously distributed. The ABA content of roots sampled from the site of high nutrient content was greater than in those elsewhere. It is suggested that this might be important for inhibition of their extension growth and stimulation of laterals in the nutrient rich patch. Heterogeneously distributed nutrients beneficially influenced accumulation of ¹⁵N and assimilation of CO₂ by the plants, enabling an increased supply of nutrients to the parts of the root system beyond the nutrient rich patch and sustained their rapid extension. Enhanced penetration of roots into the deeper soil layers could contribute to the observed increase in drought resistance of plants grown with localised placement of fertilisers under field conditions.     

A formulation of neem cake seeded with Bacillus sp. provides control over tomato Fusarium crown and root rot

Fusarium crown and root rot (FCRR) caused by the fungus Fusarium oxysporum f. sp. radicis-lycopersici is a damaging soil-borne disease of tomato. A plant growth rhizobacterium, Bacillus sp. strain HN09 isolated from neem tree rhizosphere soil, was shown to inhibit the growth, germination and development of normal morphology of the FCRR pathogen. A substantial level of disease control was achieved in greenhouse trials by soil supplementation with a preparation of neem cake seeded with HN09. Dry sterilisation of neem cake before fermentation gained comparable disease control effect as those in the unsterilised treatment, whereas moist sterilisation treatment decreased the effect significantly. This bioformulation also led to significantly raised activities in tomato genes encoding pathogenesis-related proteins, hence providing an effective alternative for the control of FCRR, reducing the need for chemical fungicide and fertilisers that impact the environment.     

Oat residue and soil compaction influences on common root rot (Aphanomyes euteiches) of peas in a fine-textured soil

Management of common root rot (Aphanomyces euteiches Drechs.) in peas (Pisum sativum L.) is sought primarily by host crop avoidance for several years. Soil compaction is known to aggravate A. euteiches disease in peas but effects on infection and subsequent symptom development are not sufficiently known to assist in cultural control. Several isolated observations have noted that oat crop residues may suppress A. euteiches infection and disease in pea roots. The individual and combined influence (a factorial combination of two factors each at two levels) of a prior oat crop and soil compaction were studied for their effects on common root rot severity in processing peas grown in an A. euteiches disease nursery on a fine-textured soil in the northern Corn Belt of the USA. A previous crop of summer oats relative to prior-year peas significantly suppressed common root rot and increased pea fresh vine weight 210% at peak bloom stage. Both fresh vine weight and green pea yield were reduced as much as 63% by soil compaction and increased as much as 48% by a prior oat crop. Greater soil bulk density at the 10 to 25-cm depth identified wheel traffic compaction patterns in each year. A 10-fold reduction of saturated hydraulic conductivity in the 10 to 25-cm compacted zone and high soil-water potentials within the upper 60 cm both confirmed an impaired water drainage, especially during infiltration events. These observations support the use of a previous full season or summer oat crop jointly with chisel plowing, plus the prevention of excessive traffic during secondary tillage and planting, to reduce common root rot in a field infested with A. euteiches. Shallow incorporation of oat shoot and root residue by chiseling could be a crucial component of the cultural control of the disease. R Rodriguez Kabana Section editor     

Evaluation of plant growth-promoting Rhizobacteria for their efficiency to promote growth and induce systemic resistance in pearl millet against downy mildew disease

Six strains of Plant growth promoting Rhizobacteria (PGPR) were tested for their ability to promote growth and induce resistance in pearl millet against downy mildew disease. All the PGRP strains showed a significant (P < 0.01) increase in growth promotion in laboratory as well as greenhouse conditions. Only two strains of Pseudomonas spp., UOM ISR 17 and UOM ISR 23, were capable of protecting pearl millet against downy mildew significantly. Pseudomonas UOM ISR 17 and UOM ISR 23 were able to offer 56.3 and 47.5%, respectively against downy mildew disease. When tested for the time gap needed to offer maximum protection, it was found that both the strains needed four days to offer maximum protection of 73.3% and 59.7%, respectively. While both the Acetobacter strains UOM Ab9 and Ab11 and Azospirillum strain UOM Az3 were able to promote growth and offered disease protection of 39.2, 22.3 and 17.40% respectively, they were not as efficient as the two Pseudomonas strains in protecting pearl millet against downy mildew. Maximum growth promotion was recorded by Pseudomonas spp. UOM ISR 17 with 33.9 cm height which was 44, 45, 42 and 46.8% more in height, fresh weight, dry weight and leaf area over the control which recorded 27 cm height, 8.1 g fresh weight, 2.1 g dry weight and 29 cm² leaf area, respectively.     

Development of black dot disease (Colletotrichum coccodes (Wallr.) Hughes) and its effects on the growth and yield of potato plants

Seed tubers of cvs Désirée and Pentland Crown with different severities of black dot were planted in 1988 and 1989 at Rothamsted in fields in 4– or 7-course rotations, respectively. Tubers treated with prochloraz (1988) or imazalil (1989) were planted in some plots, and in others Colletotrichum coccodes inoculum was added to the soil at planting. In further experiments at Mepal, Cambridgeshire in 1989 and 1990 and at Rothamsted in 1990 on sites where potatoes had not been grown for more than 15 years, large amounts of inoculum were added to the soil around disease-free seed tubers of two (1989) or three (1990) cultivars at planting. In all experiments plants were sampled during the season and the effects of treatments on disease development, growth and yield were recorded. Disease on roots, stem bases and tubers was found early in the season and was more severe on Désirée than on Pentland Crown plants from fields in 4– or 7-course rotations. Severity increased throughout the season and with increasing amounts of disease on the seed tubers, especially with Desiree. Disease was also found on plants from disease-free tubers and was more severe in 1988 than 1989. At harvest, black dot on tubers was significantly more severe from severely affected than from disease-free seed, and was most severe where inoculum, especially large amounts, had been added at planting. Fungicide treatment decreased disease early in the season but had no effect on tuber infection at harvest. In 1989 the weight loss of seed tubers during sprouting increased with increasing amounts of black dot, but the disease had little effect on plant size through the season. At harvest the yield of ware tubers (>50 mm) decreased with severe disease but total tuber yields were not significantly affected. However, at harvest in 1988 severely affected seed yielded significantly less than healthy seed. Plants grown from mini-tubers were free from disease on sites where potatoes had not been grown for at least 15 years. Inoculum applied at planting caused severe disease on all cultivars in both years, whereas disease was slight on uninoculated plants. Inoculated plants senesced early at Mepal in 1990, but there were no significant differences in total tuber yield in any experiment. However, yields of ware tubers (>50 mm) were sometimes decreased and the total tuber number per plant increased.     

Action of jasmonates in plant stress responses and development — Applied aspects

Jasmonates (JAs) are lipid-derived compounds acting as key signaling compounds in plant stress responses and development. The JA co-receptor complex and several enzymes of JA biosynthesis have been crystallized, and various JA signal transduction pathways including cross-talk to most of the plant hormones have been intensively studied. Defense to herbivores and necrotrophic pathogens are mediated by JA. Other environmental cues mediated by JA are light, seasonal and circadian rhythms, cold stress, desiccation stress, salt stress and UV stress. During development growth inhibition of roots, shoots and leaves occur by JA, whereas seed germination and flower development are partially affected by its precursor 12-oxo-phytodienoic acid (OPDA). Based on these numerous JA mediated signal transduction pathways active in plant stress responses and development, there is an increasing interest in horticultural and biotechnological applications. Intercropping, the mixed growth of two or more crops, mycorrhization of plants, establishment of induced resistance, priming of plants for enhanced insect resistance as well as pre- and post-harvest application of JA are few examples. Additional sources for horticultural improvement, where JAs might be involved, are defense against nematodes, biocontrol by plant growth promoting rhizobacteria, altered composition of rhizosphere bacterial community, sustained balance between growth and defense, and improved plant immunity in intercropping systems. Finally, biotechnological application for JA-induced production of pharmaceuticals and application of JAs as anti-cancer agents were intensively studied.