Pathogenic Variability of Lasiodiplodia theobromae (Pat.) Griffon and Maubl. Causing Mango Dieback and Screening of Mango Germplasm for Disease Resistance

Employing resistant germplasm is one of the most practical and cost efficient approach for disease management. Neverthless, use of these resistant cultivars turns to be fruitless due to persistence of diversity among pathogen populations across different agroecologies. These variations facilitate the pathogen to adapt and thrive in diverse environmental conditions. The variants within a population can alter the pace of disease progression and potentially trigger disease outbreaks in other host lines, which could undermine the cultivar stability. Furthermore, pathogenic variability studies indirectly aid in discriminating between resistant and susceptible accessions.

Five distinct isolates of Lasiodiplodia theobromae, associated with mango dieback and derived from five different mango varieties and five different districts in Kerala, were inoculated on six differential mango cultivars. Pathogenic attributes including PDI, PDS, incubation days, lesion size and virulence index were assessed. The coefficient of infection was determined to discern the landraces for their level of resistance/susceptibility towards mango dieback.

Different virulence patterns were discerned for the isolates. The range for various pathogenic parameters, including PDI, PDS, incubation days, lesion size and virulence index across different isolates, was recorded as follows: 33.33-100 per cent. 13.33-73.33 per cent, 9-17.33 days, 0.28-0.95 cm and 2.78-4.19 respectively. The parameter, virulence index indicated that the isolates KoKBn, KPB, and WMnMa were more virulent. The coefficient of infection calculated based on PDI and PDS identified the varieties Neelam, Bennet Alphonso, and Banganapally as susceptible and the remaining varieties Priyur, Muvandan, and Imam Pasand as moderately susceptible.