Pathogenic and morphological variability among the isolates of Fusarium udum (Butler) causing wilt of pigeonpea (Cajanus cajan)

Wilt is the most serious disease causing irreversible losses and lethal damage to the crop in Bihar, Jharkhand, Orissa and the West Bengal states of Eastern India. Because of the existence of high pathogen variability, management of the disease using resistant cultivars will be a challenging task. For breeding resistant varieties, knowledge of pathogen variability in the particular crop area is essential. In present study, fifteen isolates viz., Fu-9, Fu-10, Fu-27,Fu-32, Fu-42, Fu-49, Fu-63, Fu-72, Fu-73, Fu-74,Fu-75,Fu-84, Fu-86, Fu-87, Fu-97of Fusarium udum obtained from wilt infected pigeonpea plants of Bihar, Jharkhand, Orissa and West Bengal of Eastern India were assessed for the phenotypic variation. The isolates exhibited considerable variations in cultural and morphological characters viz., radial growth, mycelial color, sporulation, size and shape of macroconidia. Pathogenic variability on soil inoculated pot grown plants of pigeonpea resulted in 12.0 to 57.1 percent wilt incidence. The isolates also exhibited significant variations in symptoms like drooping of shoots, latent period, timing of fungal invasion, vascular clogging, drooping of shoots, and wilt establishment etc. Based on the wilt incidence, the fifteen isolates were distinguished into pathogenic groups. Fu- 10, Fu-27, Fu-32 and Fu-49 were found highly pathogenic and predominantly causing the typical wilt symptoms of more than one 31% wilt incidence. The present study indicates the existence of variability among isolates of vascular wilt pathogen collected from Eastern region of India.

Characterization of Fusarium Spp. Inciting Vascular Wilt of Tomato and Its Management by a Chaetomium-Based Biocontrol Consortium

Though the vascular wilt of tomato caused by the species of Fusarium is globally reported to be a complex disease in certain countries, for example, India, our studies indicated that the disease is caused by either Fusarium oxysporum f. spp. lycopersici (Fol) or Fusarium solani (FS) with the Fol being widely prevalent. In assessing the genetic diversity of 14 Fol strains representing the four Indian states by the unweighted pair group method with arithmetic averaging using Inter Simple Sequence Repeat (ISSR) amplicons, the strains distinguished themselves into two major clusters showing no correlation with their geographic origin. In pot experiments under polyhouse conditions, the seed dressing and soil application of a talc-based formulation of a biocontrol treatment, TEPF-Sungal-1 (Pseudomonas putida) + S17TH (Trichoderma harzianum) + CG-A (Chaetomium globosum), which inhibited Fol, was equally effective like the cell suspensions and was even better than the fungicidal mixture (copper oxychloride-0.25% + carbendazim-0.1%) in promoting the crop growth (52.3%) and reducing vascular wilt incidence (75%) over the control treatment, despite the challenge of inoculation with a highly pathogenic TOFU-IHBT strain. This was associated with significant expressions of the defense genes, indicating the induction of host resistance by a biocontrol consortium. In field experiments on two locations, the bioconsortium was highly effective in recording maximum mean fruit yields (54.5 and 60%) and a minimum mean vascular wilt incidence (37.5%) in comparison to the untreated control. Thus, Chaetomium-based bioconsortium demonstrated consistency in its performance across the two experiments in 2 years under the two field conditions.

Integration of salicylic acid, vermicompost and bioagent for effective management of chickpea wilt disease

Aim: The aim of the present study was to evaluate the ability of integration of salicylic acid, vermicompost and bioagent for effective management of chickpea wilt disease. Methodology: The effectiveness of salicylic acid and ZnSO4 unaided and in combination with Plant growth-promoting rhizobacteria (PGPR) and vermicompost were evaluated against Fusarium wilt of chickpea under natural condition. Three sets of experiment with nine treatments were conducted in earthen pots in completely randomized design. Ten seeds of wilt susceptible chickpea variety JG 62 were sown. Twenty-days-old plants were sprayed with salicylic acid (Set I), ZnSO4 (Set II) and distilled H2O (Set III). After 24 hr of foliar spray, the whole set of treatment was inoculated with Fusarium oxysporum f. sp. ciceri inoculums, except uninoculated control. The number of wilted seedlings in each pot for each treatment were recorded at 10, 20 and 30 days post-inoculation (dpi) and compared with uninoculated pots. Results: The combined effect of vermicompost amendment @15% and pre-inoculation treatment of salicylic acid showed 0.00, 6.67 and 6.67% wilt incidence whereas treatments having ZnSO4 as pre-inoculation foliar spray resulted in 0.00, 13.33 and 13.33% wilt incidence at 10, 20 and 30 dpi, respectively. Further, the combined treatment of 15% vermicompost along with seed bacterization and pre-inoculation foliar spray of salicylic acid showed complete protection against F. oxysporum f. sp. ciceri. The beneficial effect of vermicompost and PGPR isolate on root and shoot length, and fresh and dry weight of chickpea plants were also observed. Interpretation: High potential for integrating vermicompost, bioagent and foliar application of salicylic acid to surrogate chemical fungicides for eco-friendly and sustainable management of wilt disease in chickpea.

Phylogeny and Optimization of Trichoderma harzianum for Chitinase Production: Evaluation of Their Antifungal Behaviour against the Prominent Soil Borne Phyto-Pathogens of Temperate India

Trichoderma is the most commonly used fungal biocontrol agent throughout the world. In the present study, various Trichoderma isolates were isolated from different vegetable fields. In the isolated microflora, the colony edges varied from wavy to smooth. The mycelial forms were predominantly floccose with hyaline color and conidiophores among all the strains were highly branched. Based on morphological attributes, all the isolates were identified as Trichoderma harzianum. The molecular identification using multilocus sequencing ITS, rpb2 and tef1α, genes further confirmed the morphological identification. The average chitinase activity varied from 1.13 units/mL to 3.38 units/mL among the various isolates, which increased linearly with temperature from 15 to 30 °C. There was an amplified production in the chitinase production in the presence of Mg+ and Ca2+ and Na+ metal ions, but the presence of certain ions was found to cause the down-regulated chitinase activity, i.e., Zn2+, Hg2+, Fe2+, Ag+ and K+. All the chitinase producing Trichoderma isolates inhibited the growth of tested pathogens viz., Dematophora necatrix, Fusarium solani, Fusarium oxysporum and Pythium aphanidermatum at 25% culture-free filtrate concentration under in vitro conditions. Also, under in vivo conditions, the lowest wilt incidence and highest disease control on Fusarium oxysporum was observed in isolate BT4 with mean wilt incidence and disease control of 21% and 48%, respectively. The Trichoderma harzianum identified in this study will be further used in formulation development for the management of diseases under field conditions.

Association between Soil Acidity and Bacterial Wilt Occurrence in Potato Production in Ethiopia

Soil acidity is one of the main constraints to crop production worldwide. In Ethiopia, the problem of soil acidity has been increasing. Currently, more than 40% of cultivated land in the country has a soil pH < 5.5. Recently, bacterial wilt (caused by Ralstonia solanacearum) has become a serious problem, reaching epidemic levels in some of the major potato growing districts in the country. However, it is currently unknown if the current outbreak of bacterial wilt in potato production is associated with soil acidification or not. To examine the association between bacterial wilt and soil acidification, we conducted a field survey and field experiments and detected and characterised R. solanacearum strains. The study showed that 50% of potato fields were very strongly acidic (pH 4.5–5.0) and bacterial wilt incidence was higher in potato fields with low soil pH. The field experiments indicated that lime application significantly increased soil pH (p < 0.001) and reduced bacterial wilt incidence (p < 0.001). The more lime was applied, the stronger the positive effect on soil pH and the stronger the reduction in bacterial wilt incidence. Bacterial wilt incidence was on average 10.8% under 12 t/ha lime application, while it was about 40% in control plots (without lime) after 90 days. All R. solanacearum strains isolated from the symptomatic potato plants were Phylotype II. Our findings show that the current outbreak of bacterial wilt in Ethiopia is associated with soil acidification. They add to the understanding of the risk factors for bacterial wilt in potato. Aside from farm hygiene, sanitation and cultural practices, addressing soil acidification using lime needs to be considered as an additional component of an integrated package to deal with bacterial wilt in potato under acidic soil conditions.

​Effect of Nutrients on Wilt in Chickpea

Background: Chickpea (Cicer arietinum L.) contributes 18% of the global production of grain legume and serves as an important source of dietary protein. Fusarium wilt, caused by soil borne fungus Fusarium oxysporum f. sp. ciceri appears to be the most devastating diseases of chickpea throughout the world. It is one of the important limiting factors of chickpea production in India. The disease causes substantial yield losses which may reach even 100 per cent under favorable weather conditions. Methods: Pot culture experiments were conducted at Rajasthan Agricultural Research Institute, Durgapura, Jaipur during rabi 2014-15 and 2015-16 to study the effect of nutrients on wilt caused by Fusarium oxysporum f. sp. ciceri (Padwick) in chickpea (Cicer arirtinum). In the first experiment, the treatments comprised of four nitrogen levels-viz. 0, 15, 20 and 25 kg/ha and four phosphorus levels- viz. 0, 30, 40 and 50 kg/ha tried in sixteen treatment combinations. Surface sterilized seeds of chickpea cultivar L-550 were sown in each pot. After sowing, 400 ml water was supplied to each pot; there after watering was done at an interval of 6 days. In second experiment, the treatments comprised of 7 micronutrients viz. zinc, manganese, calcium, copper, cobalt, iron and nickel used at the rate of 10mg/kg of soil. Chickpea cultivar L-550 was used as a test crop. Result: Disease incidence was recorded periodically commencing 15 days after sowing and was continued up to 55 days after sowing. Levels of nitrogen application had increased wilt incidence successively in both the years. Whereas, a reverse trend was observed with the application of phosphorus, incidence of wilt was decreased with increasing levels of phosphorus. Application of zinc and calcium reduced the wilt incidence significantly over check. Zinc was found to be most effective in minimizing the disease incidence.

Generation Mean Analysis for Seed Yield and Wilt Resistance in Castor (Ricinus communis L.)

Background: Castor is an important non-edible oil seeds crop of Gujarat state. Yield potentiality of this crop has been considerably improved through several breeding techniques. Now days, a wilt (Fusarium oxysporum f. sp. ricini) of castor has become a serious problem. The present study therefore, was under taken to use populations of P1, P2, F1, F2, BC1 and BC2 generations in each of six crosses of castor. The six crosses were selected in such a way that two crosses in each group of resistance × resistance, resistance × susceptible and susceptible × susceptible made available for detail study of gene effects for wilt resistance.Methods: The experiment was laid out in a compact family block design with three replications during kharif, 2017. The experimental materials consisted of four pistillate lines viz., VP-1, Geeta, SKP-84 and SKP-106 and six inbred lines viz., VI-9, JI-35, 48-1, SH-72, SKI-215 and PCS-124 selected from the germplasm maintained at the Castor and Mustard Research Station, S.D. Agricultural University, Sardarkrushinagar. Each entry was planted in a single row of 10 dibbles maintaining 120 cm row to row and 60 cm plant to plant distances.Result: The analysis of variance revealed significant difference among different generations for wilt incidence and seed yield indicating considerable variability in the material tested. The estimation of the gene effects revealed that additive as well as non-additive gene effects were observed for wilt incidence and seed yield in all the six cross. In the cross, VP - 1 × JI- 35 the wilt incidence estimation of scaling test and gene effect was observed non-significant indicating non-allelic interaction was absent for this character, while for seed yield, all the crosses have significant scaling test indicating the presence of non-allelic interactions for this trait.

Efficacy of different fungicides and biopesticides for the management of lentil wilt (Fusarium oxysporum f. sp. lentis)

In Vitro and In Vivo studies on the efficacy of fungicides and biopesticides. Among the fungicides, in Carbedazim to the most effective as they have inhibited the mycelia growth completely of the test fungus, and Benomyl, Topsin - M, Ridomil,Vitavax were found the next best in inhibiting the mycelial growth of the pathogen up to 92.11% to 83.46% respectively. Sadabahar was least effective plant extracts which causes 42 mm of radial growth and inhibited the growth of the only 19.23%. In Vivo condition the maximum seed germination (95.50% and 95.33%), minimum wilt incidence (5.16% and 3.65%) and highest grain yield (10.50 q/ha and 10.35 q/ha) was found seed treatment with Carbendazim (0.2%). Among the test plant extracts Tulsi was lested effective, which show the minimum seed germination (80.00% and 77.50%), maximum wilt incidence (15.70% and 14.10%), and lowest grain yield (3.92 q/ha and 4.17 q/ha).