Pigeonpea, Phytophthora blight, Inhibition, Bioagents.

Pigeonpea [Cajanus cajan (L.) Millspaugh] is an important legume in tropical and subtropical regions. It is also known by several dialects and trade names such as red gram, tur, Angolan pea, Congo pea, yellow dhal and oil dhal. Pigeon pea is the richest source of protein, making it a recommended addition to a balanced cereal diet, especially in the absence of protein (21% in green seeds, 18.8% in mature seeds and 24.6% in dhal) and essential amino. Acids such as methionine, lysine and tryptophan. In the world, it is cultivated on approximately 4.58 million hectares and the production is 3.27 million tons. Pigeonpea, a Kharif crop native to Maharashtra, is grown in marginal areas because it can grow in water and nutrient-stressed soils. Despite the high yield potential (2000-2500 kg/ha), the actual yield is lower due to low productivity and poor management. Pigeon pea is grown mainly as an intercrop with other plants that do not receive full attention.

In addition, crops face many biotic and abiotic factors that limit its true productivity. More than 160 pathogens carry diseases to pigeon, which is a major risk in cultivation. More than 63 fungal, 3 bacterial, 19 viral or similar pathogens and 10 nematodes have been reported to infect crops at different growth stages. Few diseases in India cause significant yield loss and are economically important. The spectrum and intensity are different in different agro-climatic regions and growing situations. Fusarium wilt, sterility mosaic disease and phytophthora blight are the most common and economically important diseases in Maharashtra.

The first suspicion of Phytophthora blight in pigeonpea was reported by Williams et al. (1968). Although disease control with chemicals is very effective, growing concern about pesticide toxicity has prompted a search for alternatives. In that direction, biological control is considered to be environmentally friendly and a good alternative to sustainable agriculture to address public concerns about pathogens resistant to pesticides and chemical pesticides (Akhtar and Siddiqui 2008). The use of bioagents can reduce the emergence of insecticide-resistant pathogenic strains, which have become a major problem worldwide (Utkhede and Smith 1992).

Therefore, the use of bioagents for disease control appears to be an environmentally friendly, cost-effective and promising alternative to chemical disease control. Therefore, this study was conducted to evaluate the in vitro efficacy of effective bioagents against P. drechsleri Tucker f. sp. cajani, which causes stem blight disease of pigeonpea.

A total seven fungal antagonists viz., Trichoderma asperellum, T. harzianum, T. hamatum, T. longibrachiatum, T. virens, T. koningii, Aspergillus niger and two bacterial antagonists i.e., Pseudomonas fluorescens and Bacillus subtilis were evaluated in vitro against Phytophthora drechsleri f. sp. cajani, applying dual culture technique (Dennis and Webster 1971). Seven days old cultures of the test bioagents and test fungus (P. drechsleri f. sp. cajani) grown on Potato Dextrose Agar (PDA) were used for the study. Discs (5 mm diam.) of PDA along with culture growth of the test fungus and bioagents were cut out with sterilized cork borer. Then two culture discs, one each of the test fungus and bioagent were placed at equi-distance and exactly opposite with each other on solidified PDA medium in Petri plates aseptically. Plates were incubated at 27 ± 2 0C. PDA plates inoculated only with culture disc of the fungus were maintained as untreated control. The experimental details were as given below.

Experimental details 

Design : CRD

Replications : Three

Treatments : 10

Treatment details

Observations on linear mycelial growth of the test fungus and bioagent were recorded at an interval of 24 hours and continued till untreated control plates were fully covered with mycelial growth of the test fungus. Percent inhibition of the test fungus by the bioagents over untreated control were calculated by applying following formula (Arora and Upaddhyay 1978). 

The results presented in (Table 1, Plate I and Fig. 1) demonstrate the in vitro effectiveness of various bioagents in reducing the mycelial growth of P. drechsleri f. sp. cajani, a fungal disease that affected crops. The 10 treatments and associated pathogen colony diameters, as well as % inhibition had been presented. In addition, standard error (SE) and critical difference (CD) values at a 1% significance level are shown to assess statistical significance.

Table 1: In vitro efficacy of different bioagents on mycelial growth and inhibition against P. drechsleri f. sp. cajani.

Of the antagonists tested, T. harzianum was found most significant with highest mycelia growth inhibition (81.87 %) of the test pathogen. The second and third inhibitoriest antagonists found were T. asperellum and A.niger with inhibition of 72.00 % and 70.72 %, respectively. These were followed by T. hamatum (69.64 %), T. virens (68.17 %), T. koningii 65.56 %), T. longibrachiatum (63.33 %), P. fluorescens (54.18 %) and least inhibition of pathogen was observed in B. subtilis (39.64 %). Thus, the bioagents viz., T. harzianum, T. asperellum and A.niger were found most potential antagonists against P. drechsleri f. sp. cajani

The results of present investigation resembling the finding of earlier worker, Ambadkar and Jadhav (2007) used a dual culture technique to evaluate the efficacy of Trichoderma spp. in inhibiting the growth of Phytophthora spp. At 72 hrs of incubation the highest percent inhibition of mycelial growth of Phytophthora nicotianae was recorded in the treatment of T. harzianum (48.71%). The highest percent inhibition of Phytophthora citrophthoora was recorded in the treatment of T. viride (45.30%) at 72 hrs of incubation, followed by T. lignomm (40.88%) and T. harzianum (38.12%). Vijayaraghavan and Koshy (2007) evaluated the efficacy of efficient antagonist from black pepper nurseries and use them alone or in the combination with soil solarization fungicides in the integrated management of Phytophthora diseases in black pepper nursery. Among the different native fungal isolates, two were found to be effective and were identified as Trichoderma viride and Trichoderma longibrachiatum observations on the incidence and severity of Phytophthora tot in black pepper nursery found that in general soil solarization, application of native fungal antagonists and spraying of Ridomil MZ had a favourable effect in evaluating the disease. It was also found that solarization of potting mixture and application of Trichoderma spp. and a positive effect in minimizing the mortality of cuttings. 

Plate I: In vitro efficacy of different bioagents against P.  drechsleri f.sp.cajani.

Fig. 1. In vitro efficacy of different bioagents against P. drechsleri f. sp. cajani.

J.B. Bhalerao, P.H. Ghante, S.N. Banne, J.D. Sirsat, P.B. Bhalerao and S.S. Kadam  (2024). In vitro efficacy of Biocontrol Agents Against Phytophthora drechsleri Tucker f. sp. cajani, causing Stem Blight Disease of Pigeonpea. Biological Forum – An International Journal, 16(6): 156-158.