Interaction of Meloidogyne incognita and fungi: a potential threat to cotton crop in Punjab

Cotton is an important cash crop of Pakistan and is severely affected with wilt in cotton-growing areas of Punjab province. Research was carried out on two major pathogens of cotton Fusarium oxysporum f. sp. vasinfectum and Meloidogyne incognita and their possible role in wilt disease complex. During 2017-19, a survey of cotton growing areas of Punjab (Jhang, Multan, Vehari, Mianwali, Rahim Yar Khan, Bahawalpur, Kabir Wala, Dakota, Basti Dharik, Tibba Sultan Pur, Rajan Pur, Chak 27 (Layyah), Chak 99B (Layyah), Lodhran, Fateh Pur and Dagar Rohtass) was conducted to collect a sample on symptomology basis of yellowing of leaves, discoloured bark of lower part of the stem, blackened xylem vessel and wilting. Data were recorded on wilt disease incidence, prevalence, associated pathogens and root-knot nematodes. Prevalence of cotton wilt was recorded the maximum 85% in areas of Vehari, Kabir Wala and Rajan Pur while the maximum incidence in both Multan and Tibba Sultan Pur was 15%. Percentage association of wilting fungi was recorded from the soil, roots, stem and leaves on placing them in artificial media and soil dilution techniques were used to determine fungi in rhizosphere such as Fusarium oxysporum, Verticillium spp., Penicillium spp., Aspergillus spp., Rhizoctonia spp., Colletotrichum spp., Rhizopus spp., Mucor and Pythium. Root associated fungi were isolated by Hyphal tip method and isolated F. oxysporum, Rhizoctonia spp. and Pythium spp. From stem and leaf sample, F. oxysporum, Verticillium spp., Colletotrichum spp., Alternaria spp. and Botryodiplodia spp. were recorded. Relative density nematode was recorded from different locations and highest occurrence was observed in Bahawalpur (85%) by using different extraction methods. Eggs masses of root knot nematodes were staining by using Phloxin B and nematodes inside root system was done by using acid fuchsin. Nematode reproduction parameters like No. of J2/roots system, J2 in 100ml of soils, eggs masses/root system, females/ roots system, galls/ root system were recorded. Cotton wilt caused by the interaction of Fusarium and Root knot nematode is threat to cotton industry in Pakistan and it should be treated to avoid economic losses.

Saccharothrix Algeriensis NRRL B-24137 Potentiates Chemical Fungicide Carbendazim in Treating Fusarium Oxysporum f.sp. Vasinfectum-Induced Cotton Wilt Disease

Cotton ( Gossypium hirsutum) wilt is one of the destructive disease caused by Fusarium oxysporum f. sp. vasinfectum and lead to 100% yield loss under favorable conditions. This study aims to estimate the potential of biological control agents Saccharothrix algeriensis NRRL B-24137 (SA) and chemical fungicides against cotton wilt pathogen under in-vitro and in-vivo conditions. The in-vitro study revealed that carbendazim showed maximum mycelia growth inhibition with a mean of 91% over control, which was further validated in glasshouse assay. In-vitro dual culture test of biocontrol agents with F. oxysporum determined that SA had a potential to inhibit mycelia growth by 68% compared to control. Further in glasshouse assay, the combination of the SA and carbendazim (10 µg/mL) showed a significant ( p < 0.05) disease control. Moreover, results demonstrated that carbendazim and SA remarkably decreased the disease development up to 83% and subsequently, significant improvement was observed in the plant growth parameters (plant length, root length, and plant weight) compared to untreated plants. Conclusively, exploration and utilization of bioagent for fungal diseases in cotton may provide a better line with maximum efficacy and with lesser adverse effects, which will pave a way toward better consequences in fungal treatments.

Detection and Characterization of Fusarium oxysporum f. sp. vasinfectum VCG0114 (Race 4) Isolates of Diverse Geographic Origins

A highly virulent cotton wilt pathogen, Fusarium oxysporum f. sp. vasinfectum VCG0114 (race 4) was found in West Texas in 2017, after being known in California since 2001. Isolates obtained from wilted plants collected in 2017 from Texas, in 2015 from China, and during 2001 to 2014 from California and isolates from historical collections including the race 4 reference isolate were characterized by soil-infestation pathogenicity assays, DNA sequence analysis, and vegetative compatibility analysis. All obtained F. oxysporum f. sp. vasinfectum isolates belonged to VCG0114. All of these isolates, except one isolate from China, caused disease in a soil-infestation assay without nematodes. Thus, they belong to the nematode-independent pathotype. Texas isolates were significantly more virulent than were isolates from China or California on Gossypium barbadense ‘Pima S-7’. Four different genotypes (N, T, MT, and MiT) were identified based on the transposable element Tfo1 insertion into the PHO gene and independent MULE or MITE insertions into the Tfo1 transposon. Some significant differences in virulence were detected among the genotypes in some locations. No differences in pathogenicity were observed between the California and China collection isolates on Pima S-7, and the virulence of the major genotypes was similar on the Gossypium hirsutum cultivar ‘Stoneville 474’ or the Barbren 713 germplasm line. Simple polymerase chain reaction (PCR) methods were developed to specifically determine and detect the four genotypes within VCG0114. A specific PCR method to detect all VCG0114 isolates was also developed. These methods will facilitate the timely identification of infested fields and seed lots and the elucidation of evolutionary relationships among the isolates. This should help to closely monitor the movement of the pathogen and reduce dissemination of these devastating pathogens.

Determination of the Response of Some Cotton Varieties to Cotton Wilt Disease Caused by Verticillium dahliae Kleb

Verticillium Wilt Disease is one of the most important diseases affecting the rate of cotton yield. There is no economic chemical control for Verticillium wilt, but it is recommended to use resistant varieties to control this disease. This experiment was carried out in a randomized plot design with four replications in the growth chamber to determine the response of some cotton cultivars against a defoliating and non-defoliating pathotypes of Verticilllium dahliae Kleb. In the study, a total of twenty cotton cultivars i.e. the resistant control GIZA 75, the tolerant control CARMEN and the susceptible control ACALA SJ2, defoliating (PYDV6 isolate) and non-defoliating (Vd 11 isolate) pathotypes were used, and cotton varieties were tested using conidial suspension technique. Analysis of variance showed significantly (P

Genetic Diversity, Virulence, and Meloidogyne incognita Interactions of Fusarium oxysporum Isolates Causing Cotton Wilt in Georgia

Locally severe outbreaks of Fusarium wilt of cotton (Gossypium spp.) in South Georgia raised concerns about the genotypes of the causal pathogen, Fusarium oxysporum f. sp. vasinfectum. Vegetative complementation tests and DNA sequence analysis were used to determine genetic diversity among 492 F. oxysporum f. sp. vasinfectum isolates obtained from 107 wilted plants collected from seven fields in five counties. Eight vegetative complementation groups (VCG) were found, with VCG 01117B and VCG 01121 occurring in 66% of the infected plants. The newly recognized VCG 01121 was the major VCG in Berrien County, the center of the outbreaks. All eight VCG resulted in significant increases in the percentages of wilted leaves (27 to 53%) and significant reductions in leaf weight (40 to 67%) and shoot weight (33 to 60%) after being stem punctured into Gossypium hirsutum ‘Rowden’. They caused little or no significant reductions in shoot weight and height or increases in foliar symptoms and vascular browning in a soil-infestation assay. Soil infestation with Meloidogyne incognita race 3 (root-knot nematode) alone also failed to cause significant disease. When coinoculated with M. incognita race 3, all VCG caused moderate to severe wilt. Therefore, the VCG identified in this study belong to the vascular-competent pathotype, and should pose similar threats to cotton cultivars in the presence of the root-knot nematode. Use of nematode-resistant cultivars, therefore, is probably the best approach to control the disease in Georgia.