Mango varietal response to Anthracnose disease and its post-harvest management

Abstract

The study entitled “Mango varietal response to anthracnose disease and its post-harvest management” was done to evaluate the incidence and severity of anthracnose in different mango varieties during post-harvest storage and assess the efficacy of certain post-harvest management techniques controlling anthracnose on the quality of fruits in different mango varieties. A survey was conducted in two agro-ecological units – 1 (Southern coastal plain) and 8 (Southern laterites) covering Kollam and Thiruvananthapuram districts. Mango varieties with anthracnose symptoms were collected from the surveyed locations, and pathogen isolates were obtained. The isolates were subjected to pathogenicity testing, morphological characterization, and virulence rating. The cultural and morphological studies showed that isolates displayed fluffy or sparse mycelial growth with white to grey pigmentation and had regular margins. The conidia of all isolates were oblong, dumbbell shaped, measuring 9.2 × 3.5 to 11.4 × 3.6 μm. Upon artificial inoculation on the fruits, the isolates showed the typical anthracnose symptoms, with black or brown sunken lesions. Upon virulent rating, it was revealed that isolate C10 proved to be the most virulent, with a lesion development rate of 1.30 cm/day and PDI of 46.67%. The virulent isolate was molecularly characterized with ITS primers and confirmed as Colletotrichum gloeosporioides (accession no. PQ475860) by phylogenetic analysis. Five mango varieties, Kottukonam, Neelum, Priyur, Rumani, and Totapuri, were obtained and subjected to screening by artificial inoculation of the anthracnose pathogen and assessed the varietal variation in symptom development, lesion growth and susceptibility. Symptoms were developed in 2 days for Kottukonam and Priyur, while Neelum, Rumani, and Totapuri showed symptoms after 3 days. Kottukonam showed the highest susceptibility with a PDI of 72.33%, while Totapuri had the lowest at 45.40%. In vitro evaluation of the antagonistic potential post-harvest management strategies against anthracnose pathogens was studied. Two bacterial cultures of Bacillus velezensis PCSE-10 and B. amyloliquifaciens VLY24 were obtained from the Department of Agricultural Microbiology. The dual culture assay of the biocontrol agents against the anthracnose pathogen revealed that B. amyloliquifaciens VLY24 showed 37.08% inhibition, while B. velezensis PCSE-10 had 32.87% inhibition. Poisoned food assay of carbendazim 50% WP against the pathogen revealed that 0.1% and 0.2% concentration showed 100% inhibition while 0.05% showed 76.67% inhibition. In vitro evaluation of bacterial suspension and cell free culture filtrate (CFC) of biocontrol agents against the pathogen mycelial growth at different concentrations showed that bacterial suspensions were more effective than CFC. In both the strains highest inhibition of mycelial growth was shown in the bacterial suspension of 100% concentration with 78.78% inhibition with B. amyloliquifaciens VLY24 and 76.83% inhibition with B. velezensis PCSE-10. The evaluation of various post-harvest management strategies for controlling anthracnose disease was conducted in five mango varieties in a two-factorial Completely Randomized Design (CRD). It revealed that the combination of hot water treatment (HWT) (52°C for 10 minutes) + B. amyloliquefaciens VLY24 (BA VLY24) (100% suspension) and carbendazim (CBZ) (0.1%) resulted in the lowest per cent disease index (PDI) of 17.04%, followed by the combination of HWT (52°C for 10 minutes) + B. velezensis PCSE-10 (BV PCSE-10) (100% suspension) + CBZ (0.1%), which had a PDI of 18.68%. Among the varieties, the lowest PDI was observed in Totapuri (38.26%), while the highest was recorded in Kottukonam (46.56%). Regarding total soluble solids (TSS), the combination of HWT+ BA VLY24 + CBZ recorded the lowest TSS content (12.86 °Brix). Across varieties, Priyur exhibited the highest TSS content (17.63 °Brix), followed by Neelum (14.65 °Brix). The effects of the interaction of treatments on lesion size and PDI across all varieties were not significantly different, which implies that treatments applied across all varieties have the same relative effect, whereas the impact on TSS varied significantly among varieties as TSS content varies with varieties. A combination treatment of hot water (52°C for 10 minutes) +B. amyloliquefaciens VLY24 (100% bacterial suspension) + Carbendazim 50% WP (0.1%) was applied to five mango varieties (Kottukonam, Neelum, Priyur, Rumani, and Totapuri). The response of treated fruits was compared with untreated controls. On the 7DAI, no symptoms were observed in treated fruits except for Kottukonam, whereas untreated fruits displayed symptoms as early as the 4th or 5th day. PDI was significantly higher in untreated fruits, with the highest PDI recorded in untreated Kottukonam (50.67%) and the lowest in untreated Totapuri (22%). Biochemical analysis revealed that peroxidase and polyphenol oxidase activities were higher in treated fruits than untreated ones on the 7 DAI. Treated fruits also exhibited an extended shelf life, and Totapuri recorded the longest duration (9.33 days). Physiological loss of weight was higher in untreated fruits than in treated fruits. Sensory evaluation revealed that treated fruits exhibited superior internal and external sensory quality in terms of appearance, colour, flavour, and overall acceptability. Among the varieties, Totapuri received the highest overall acceptability score of 8.08. Biochemical assessments indicated that treated fruits had higher titratable acidity whereas, total soluble solids (TSS) and reducing sugar content were lower in treated fruits across all varieties tested. This study concluded that C. gloeosporioides was the pathogen responsible for mango anthracnose. Among the varieties, when subjected to screening by artificial inoculation, it revealed that Kottukonam was the most susceptible mango variety, followed by Priyur, while Totapuri was the least susceptible, followed by Rumani and Neelum. Effective post-harvest management of mango anthracnose can be achieved using a combination of hot water treatment (52°C for 10 minutes), B. amyloliquefaciens VLY24 (100% suspension), and carbendazim 50% WP (0.1%).