Influence of Weather Parameters on the Incidence and Severity of Guava Scab Caused by Pestalotiopsis psidii (Pat.)

Guava (Psidium guajava) is an important tropical fruit crop of India and is known as “apple of the tropics”. It is grown and utilized as an important fruit in tropical countries like India, Indonesia, Pakistan, Bangladesh and South America. Among the biotic and abiotic diseases of guava, guava infected by scab disease [Pestalotiopsis psidii (Pat.) Mordue] is an economically important and reported average yield losses in the range of 12-18%. An experiment was conducted during 2023 at Horticulture garden, Main Agricultural Research Station, University of Agricultural Sciences, Raichur during 2023 to understand the influence of various weather parameters on the guava scab disease development. The results revealed that, irrespective of the varieties, interaction among maximum temperature, minimum temperature, maximum relative humidity, minimum relative humidity, rainy days and rainfall showed significant positive correlation with guava scab disease. And the incidence and severity of guava scab was found to be 23.21, 56.00 (Allahabad Safed), 32.45, 68.50 (Lucknow 49) and 85.00, 74.51 (Arka Kiran) respectively.

Studies on Symptomatology, Morphological and Molecular Characterisiation of Erysiphe cichoracearum Causing Powdery Mildew of Okra

Okra (Abelmoschus esculentus (L.) Moench) is a globally important annual vegetable belongs to family malvaceae, it is most broadly distributed vegetable all over the world. Among the fungal diseases affecting okra crop, powdery mildew caused by Erysiphe cichoracearum DC. is the most important disease causing considerable yield losses. The disease was characterized by the appearance of small white powdery specks on upper surface of the lower leaves which enlarged and coalesced forming bigger patches. Later on the disease spread to the upper leaves, coalescing of the white powdery specks and enlargement in their size ultimately resulted in complete coating of white fungal mass on the leaves. The morphological studies of the pathogen in the laboratory revealed, that the mycelium is septate, ectophytic, hyaline and adjacent to the mycelium, basal septum of the conidiophores was seen. The conidiophores were erect, on which conidia were produced either singly or in short chains. The conidia were found cylindrical or barrel in shape, hyaline, non-septate and measured 75.23 µm x 40.65 µm. Molecular characterisation of the native isolate resulted in the DNA amplicon at the region 531 bp. Further, DNA sequence was obtained for ITS Rdna and was deposited in NCBI gene bank. Accession number ‘MW774352’ was obtained and it was confirmed that the causal pathogen of okra powdery mildew of Raichur region is Erysiphe cichoracearum.

Correlation of Weather Variables on Emergence of a Virus Disease Bud Necrosis Disease of Greengram Incited by Soybean Yellow Mottle Mosaic Virus at Raichur, Karnataka

Greengram [(Vigna radiata (L.) Wilczek] is the important pulse crop after chickpea and pigeonpea cultivated in India which is called as “Queen of pulses”, the crop is proned to be infected by many fungal and bacterial diseases. In recent years emergence of a virus disease bud necrosis of greengram was noticed in Raichur and the incidence of disease gradually increased in greengram growing areas of Karnataka. Incidence of bud necrosis disease of greengram and correlation with weather factors was studied during Kharif 2021 at research plot and MARS, UAS, Raichur, Karnataka. The study reveals that, on all four dates of sowing (25th June, 1st July, 9th July and 23rd July 2021), disease was initiated at 25 DAS and highest disease incidence was observed at 75 DAS. The peak activity of thrips was noticed during August month. The weather variables viz., maximum temperature was more than 32 °C, minimum temperature was more than 22°C, rainfall was less than 19 mm/day, morning relative humidity was less than 91 per cent, evening relative humidity more than 44 per cent, evaporation 4.3 mm/day and sunshine hours less than 6 hr/day was favorable for bud necrosis disease in four dates of sowing. Whereas, morning relative humidity, evening relative humidity and age of the crops were having positive relationship with progress of bud necrosis on all four dates of sowing. Thrips and rainfall showed a positive correlation with disease incidence in all dates of sowing except the fourth date of sowing.