Variability and Virulence Analysis of Aspergillus niger Isolates Causing Collar Rot of Groundnut

Background: Collar rot of groundnut (Arachis hypogaea L.) caused by Aspergillus niger is a significant constraint in groundnut cultivation and responsible for huge economic losses in India including Rajasthan. Methods: By surveying of eight major groundnut growing districts of Rajasthan, India, one representative Aspergillus niger isolate from each district was established (ANBK-01= Bikaner, ANCH-02= Churu, ANDA-03= Dausa, ANJP-04= Jaipur, ANJL-05= Jalore, ANJD-06= Jodhpur, ANNG-07= Nagaur and ANSK-08= Sikar) for studying variability in the pathogen as well as to know the response of groundnut varieties to the highly virulent isolate. The colony and spore characteristics were observed for cultural and morphological variability. For resistance response to the disease, ten varieties (M-13, RG-633-9, RG-382, Girnar-2, RG-604, RG-578, Gajraj 10, RG-510, RG-632-1 and RG-644) were evaluated in the field for two consecutive years against a highly virulent Aspergillus niger (ANJP-04) isolate. Result: Our investigations cleared that all the isolates were showed cultural and morphological variability such as shape, colour and size of colony and size of conidia, conidiophores and columella. Isolate (ANJP-04) collected from Khejroli village of Chomu tehsil in Jaipur district showed maximum mycelial growth, conidia diameter, length and diameter of conidiophores and length and diameter of columella, early sporulation and found most virulent as it produced higher disease incidence (54.43%). Ten released varieties of groundnut in the field conditions, revealed that none of the variety was found completely free from the disease whereas RG-644, M-13 and RG-510 were found resistant while RG-604, Girnar-2, Gajraj-10 and RG-632-1 were found moderately resistant and rest were found susceptible to highly susceptible to the disease. Conclusively, it can be finalized that famers may cultivate these resistant varieties in areas where collar rot is a severe constraint. The conclusion of this study can also be utilized to screen varieties/genotypes of groundnut against highly virulent isolate for sustainability of breeding material to the disease effectively.

Forecasting model for disease risk period in chickpea x collar rot pathosystem

Collar rot caused by Sclerotium rolfsii Sacc. is one of the major biotic constraints of chickpea production worldwide. It is soil-borne fungi having wider host range and infection mainly occurs at the juvenile stage of crop growth resulting crop failure in no time. The pathogen is greatly influenced by soil temperature (ST) and soil moisture (SM) therefore, experiment formulated to develop a suitable forecasting model for its future use in computer simulation of plant disease prognostication by feeding only soil temperature and moisture data. The popular desi type chickpea variety Anuradha sown at different dates to get a range of soil temperature and soil moisture combination and its corresponding effect on disease incidence was recorded under natural epiphytotic conditions. The data obtained were analyzed using binary logistic regression and discriminant analysis to assess disease risk and non-risk period. The model developed was Y'= -73.9 + 1.251 SM + 0.017 ST. The outcome recorded, a unique statistically significant contribution of soil moisture (p value=0.029) on the establishment of the disease whereas, the effect of soil temperature was detected as statistically non-significant. The model developed and the correctness of the model determined to predict the disease severity with 80 % accuracy.

First Report of Lasiodiplodia pseudotheobromae Causing Collar Rot of Peanut in Shandong Province, China

In August 2019, a collar rot of peanut was observed in several fields in Qingdao, Shandong province, China. Disease survey was conducted in several peanut fields. Less than 5% plants exhibited various symptoms, including brown or black stem rot, pod rot, leaf chlorotic, wilted, and even dead. Symptomatic stems were cut into small pieces, surface disinfested with 70% ethanol for 1 min, 1% NaClO for 2 minutes, rinsed three times with sterile water, and dried on sterile filter papers. Pieces then were plated on potato dextrose agar (PDA) media and incubated at 25°C in darkness. Fungal cultures were initially white, then turned gray, and eventually turned black, and aerial hyphae were dense, fluffy. Conidia were ellipsoidal, initially hyaline, unicellular, 14.3 to 21.1 × 8.7 to 13.2 µm (n = 50), and mature conidia showed dark brown, with a central septum, and longitudinal stripes. Molecular identification was performed by sequencing ITS with ITS1/ITS4 (White et al., 1990) and beta tubulin gene with Bt2a/Bt2b (Glass and Donaldson, 1995) of a representative isolate ZHX9. ITS and beta tubulin regions (OK427342 and OK489788) of ZHX9 obtained 99.62 and 100% similar to L. pseudotheobromae (KF766193 and EU673111), respectively. Phylogenetic analysis was done using Neighbor-Joining (NJ) analysis based on those gene sequences. The microorganism we have isolated was identified as L. pseudotheobromae based on molecular analysis and morphological characteristics. For pathogenicity assay, twelve ten-days-old peanut (Zhonghua No.12) seedlings were each inoculated with one mycelial plug (8 mm in diameter) by placing the inoculum on the base of the stem. Twelve plants were each inoculated with a plug of non-colonized PDA as controls. Plants were incubated in a growth chamber (30°C in the day and 25°C at night, a 12-h photoperiod and 80% RH). Necrotic lesions were observed on stems of all inoculated seedlings 5 days after inoculation, whereas control plants remained asymptomatic, and L. peudotheobromae was consistently re-isolated from symptomatic stem. In Asia, peanut collar rot caused by L. teudotheobromae has been reported in India, Indonesia, North Vietnam (Nguyen, et al., 2006) and China (Guo, et al., 2014), but collar rot caused by L. pseudotheobromae has not been reported. To our knowledge, this is the first report of L. peudotheobromae causing collar rot on peanut in China. These results will provide crucial information for studying on epidemiology and management of this disease.

Influence of weather factors, soil temperature and moisture on collar rot disease of betel vine (Piper betle L.) under coastal saline zone of West Bengal

A study was conducted to find out the influence of weather factors, soil temperature and soil moisture on the incidence of Sclerotium rolfsii Sacc. induced collar rot disease in betelvine (Piper betle L.), during 2016 to 2018. Fourteen soil and weather factors, taken from the agrometeorological observatory located at instructional farm of Ramkrishna Ashram Krishi Vigyan Kendra, Nimpith and recorded from a nearby betelvine boroj, were subjected to multiple regression, binary logistic regression and canonical discriminant analysis to develop a suitable disease forewarning model. The binary logistic model, Y(0/1) = 5.899 + 0.865 (Tmax) – 0.569 (SM) + 0.097 (BRHmin) was able to predict the disease risk with 78 per cent accuracy and correctly classified 94 per cent of cases during model validation in 2018. The weekly averages of maximum temperature (Tmax), soil moisture (SM) and minimum relative humidity inside the boroj (BRHmin) were found to be the most significant predictors of disease incidence, in this model. The soil moisture at 69 - 72 per cent of field capacity, minimum temperature of 25 - 27oC, maximum temperature of 33 - 36oC, average soil temperature of 28 - 30oC, minimum relative humidity of 60 - 72 per cent inside the boroj and maximum relative humidity of 83 - 89 per cent inside the boroj were found to be highly congenial for collar rot disease incidence in betelvine under coastal saline zone of West Bengal.

Characterization and pathogenicity of Pythium-like species associated with root and collar rot of kiwifruit in Turkey

During the period of June to October in 2018, a widespread decline was observed on kiwifruit vines in the vineyards located in Altınordu, Fatsa, and Perşembe districts of Ordu province. The symptoms were associated with reddish-brown rots expanding from the root to the collar with sparse off-color foliage. Based on the percentage of the total infected samples across 18 vineyards, the most common oomycete species were Globisporangium intermedium (37.1%), Phytopythium vexans (34.3%), G. sylvaticum (14.3%), G. heterothallicum (11.4%), and Pythium dissotocum (2.9%). The morphological identification of isolates was confirmed based on partial DNA sequences containing the nuclear rDNA internal transcribed spacer region (rDNA ITS) and the mitochondrial cytochrome c oxidase subunit II (coxII) gene. The optimum growth temperature and the optimum pH of 5 species ranged from 22.98 to 28.25°C and 5.67 to 8.51, respectively. Pathogenicity tests on the seedlings of kiwifruit cv. Hayward revealed significant differences in virulence among isolates. Phytopythium vexans and G. sylvaticum isolates caused severe root and collar rot resulting in seedling death, while G. heterothallicum and G. intermedium isolates had relatively lower virulence. All Globisporangium spp. and P. vexans isolates significantly decreased plant growth parameters (plant height, shoot and root dry weights and root length); however, P. dissotocum caused very mild symptoms and did not affect these parameters of growth. To our knowledge, this is the first study reporting G. sylvaticum, G. heterothallicum, and G. intermedium causing root and collar rot on kiwifruit not only in Turkey but also in the world.

PATHOGENIC DISEASE OCCURRENCES IN PLANTATION SITES OF BASTAR DISTRICT, CHHATTISGARH, INDIA

The investigation on “Pathogenic disease occurrence in plantation sites of Bastar district, CG, India” revealed that the several disease of Tectona grandish and Eucalyptus globules trees species in the plantation site maintained by Bastar forest division (C.G.) During the survey of plantation sites, many trees were infected by pathogens. The infected teak species showed leaf spot, leaf blight, leaf gull, leaf brown spot, stem canker, powdery mildew etc. and affecting the growth and form of teak. Whereas in Eucalyptus trees showed stem canker, collar rot, leaf spot, leaf rust, brown leaf spot, disease and affecting the growth and forms of Eucalyptus. The survey was conducted at two plantation sites namely Titrgaon and Bastar in the region and incidence of pathogenic disease commonly found and casual organism/ pathogen were identified prescribed disease management was recorded. Management of immediate removal of infected plants helps to prevent the disease spread. Therefore, the present investigation was carried out for knowing occurrence and abundance of pathogens associated with Teak and Eucalyptus trees plantation in the Bastar district of Chhattisgarh.

​​Eco-friendly Management of Collar Rot of Lentil by Introduced Native Rhizobacterial Candidates

Background: Collar rot is an important disease of lentil in India and causes significant yield loss annually. Considering the recent focus on the development and use of environmentally feasible management strategies, the objectives of the study was to identify resistant sources and evaluation of native antagonists as well as plant growth promoting rhizobacteria (PGPRs) in yield improvement and disease management of lentil. Methods: Eleven popular lentil varieties were screened for resistance/susceptibility reaction against collar rot in vivo. The efficacy of two bacterial and fungal biocontrol agents (BCAs) was tested against a virulent isolate of Sclerotium rolfsii. Four PGPRs were also evaluated to study their influence on the growth parameters as well as their ability to manage S. rolfsii. Result: Three genotypes were found to be tolerant, four genotypes were moderately susceptible, while four genotypes were highly susceptible. Among the BCAs, the highest average inhibition % was observed in treatment with Bacillus sp. Among the PGPR treatments, Rhizobium in combination with phosphate solubilizing bacteria and Trichoderma or Bacillus was the most effective in controlling the collar rot when used as seed treatment and hence can be used for disease management.