Potato (Solanum tuberosum L.) belongs to the family solanaceae is the most important crop among the vegetables. The crop stands prime position in the economy of poor and marginal farmers and plays a vital role in nutritional security by producing more bio-mass per unit area as compared to wheat, rice and maize in a short period of time. Potato is considered as "The King" of staple foods. It is the only non-cereal food crop to command such a high position in the world. It is a rich source of calories and about 100 grams fresh weight of potato tuber yields 97 kilo calories, which is much higher than cereals. Potato is a good source of other nutrients like carbohydrates 20.60 per cent, protein 2.10 per cent, fat 0.30 per cent, 1.10 per cent crude fiber and 0.90 per cent ash.  It also contains good amount of essential amino acids like leucine, tryptophan and isoleucine (Yadav and Srivastava 2014). Potato being a short duration crop gave ample and economical tuber yield in 80-90 days. In India it is grown over an area of 2176 ha ('000 Ha) with the production of 49344 MT ('000 MT) and an average national yield per hectare is 23.00 tonnes (Anon., 2017). An area under potato cultivation in Karnataka is 44,000 hectares with a total production of 6.98 lakh tonnes with productivity of 13.74 tonnes per hectare. 

Potato production is currently threatened by a number of biotic and abiotic factors. Among the biotic stresses, fungal  diseases such as late blight (Phytophthora infestans), early blight (Alternaria solani), powdery scab (Spongospora subterranea), wart (Synchytrium endobioticum), watery wound rot (Pythium ultimum), silver scurf (Helminthosporium solani), pink rot (Phytophthora erythroseptica), dry rot (Fusarium spp.), black scurf (Rhizoctonia solani), skin spot (Polyscytalum pustulans), wilt of potato (Verticillium sp.) and charcoal rot (Macrophomina phaseolina) were the most destructive fungal diseases. which has reduced the quality, quantity and market value of potato tubers. (Abbas et al., 2013). Among the fungal diseases, early blight is one of the most destructive disease of potato. The disease can damage both potato foliage and tubers and also cause yield loss up to 5 to 50 per cent. An early blight disease is prevalent at worldwide wherever potatoes, tomatoes, peppers and egg plants were grown. An early blight is a polycyclic disease that can cause more than one disease epidemics within a single cropping season (Tsedaley, 2014). An early blight of potato is caused by two pathogens viz., Alternaria solani (Jones & Grout) and Alternaria alternata (Fr.) Keissler, but in some areas only A. solani is considered as the causative organism of this disease. With their spores in abundance in the atmosphere and in the soil, the disease is always a threat when conditions become conducive for infection and thus represents a serious threat to potato production (Iglesias et al., 2007, Leiminger and Housladen 2012). 

Depending upon the variety grown, weather condition and inoculum load in the soil this disease can cause an average annual yield loss of approximately 79 per cent of the total production of potato (Yadav et al., 2017). For effective management of this disease in early stage of crop growth, there is a need of management approaches in order to reduce the disease severity with increased tubers yield. Therefore, by considering the above factors the present investigation was taken for the management of early blight of potato by host range studies and germplasms as a resistance source. 

Survey for the severity of early blight in major potato growing areas of Southern Karnataka

A roving survey was conducted during kharif 2018-19 in different potato fields of Hassan and Chikkamagaluru districts and in rabi season in the fields of Kolar and Chikkaballapur districts, respectively. In each taluka five villages and in each village five fields were selected randomly. In each field randomly ten plants were examined and observations were recorded using 0-9 scale (Mayee and Datar 1986).

The details of disease rating:

Host range study of A. solani (AS3) on solanaceous crops. The host range of A. solani was studied on different solanaceous crops. The seeds of tomato (Solanum lycopersicum), capsicum (Capsicum annuum), chilli (Capsicum annum L.) and brinjal (Solanum melongena) were sown in pro-trays filled with cocopeat. The pots were filled with fertile soil, which was mixed with well decomposed FYM. About 25 days old seedlings were transplanted to the pots and five plants were maintained in each crop. Ten days old mycelial culture of A. solani was taken and mixed in one liter of sterile water and sprayed on 45 days old seedlings. The control (check) plants were maintained by spraying sterile water. Further, protected the inoculated seedlings with polythene sheet for 48 hours. A daily observations were made to check the symptoms initiation and development, PDI was calculated based on the symptom development.

Screening of potato germplasm for early blight disease. The natural incidence of early blight was recorded on different potato germplasm grown in field conditions at Horticulture Research and Extension Centre, Hassan and artificial inoculation was done in polyhouse condition at College of Horticulture, Bengaluru during 2018-19. About twenty potato genotypes were collected from the Central Potato Research Station, Jalandhar, Punjab under AICRP on Potato, Hassan were screened against early blight disease. An observations were recorded after the appearance of disease at an interval of 15 days by following 0 to 9 scale given by Mayee and Datar (1986).

The various genotypes were arbitrarily categorized into six different reactions group as follows.

Survey for the severity of early blight disease in major potato growing areas of Southern Karnataka. A roving survey was conducted during kharif and rabi 2018 to assess the severity of early blight of potato in major potato growing districts of Southern Karnataka viz., Hassan, Chikkamagaluru, Kolar and Chikkaballapura.

The data revealed that among different talukas surveyed, severity of early blight was found higher in Mulabagilu taluk with disease severity of 29.92 per cent followed by Kolar (21.60%) and Shidlaghatta (20.52%) of Kolar and Chikkballapura districts, respectively. The lowest disease severity was noticed in talukas like Kadur (5.72%) and Channarayapatna (6.75%) of Chikkmagaluru and Hassan districts respectively. Among the villages, highest disease severity was registered in Khadripura (31.12%) and Maraktani (30.21%) of Mulabagilu taluk and Girnalli of Kolar taluk (30.90%). The least disease severity was revealed in Kalyadi of Arsikere taluk in Hassan district and Belaguli of Channarayapatna taluk in Hassan district showed disease severity of 5.00 per cent in both the villages followed by Balliganavuru of Kadur taluk belongs to Chikkamagalur districts with disease severity of 5.30 per cent. Of different districts, Kolar district recorded highest per cent disease severity of 19.92 per cent followed by Chikkaballapura with disease severity of 16.42 per cent (Fig. 1 and Plate 1a  & 1b). However, Chikkamagaluru and Hassan districts were showed comparatively lower disease severity of about 6.23 and 7.56 per cent, respectively.

Fig. 1. Survey on disease severity of early blight of potato in Southern Karnataka during 2018-19.

Plate 1.

The highest per cent disease index in Kolar was due to the favourable environmental and pathogen factors. Further, it was observed that continuous growing of alternate host crops in the same piece of land has also led to over loading of the pathogen factors in the field. The changes in weather conditions and amount of initial inoculum of Alternaria solani may be responsible for varying disease intensities at different locations (Vanderwalls et al., 2003). The high relative humidity, rainfall or dew accumulation in the atmosphere can increase conidial germination and pathogen infection (Rotem, 2004). An alternative low and high humidity conditions have also been showed to favour disease development. These observations were supported by Bains et al. (2000); Prasad (2002); Hossain et al. (2010). Rao et al. (2016) reported that early blight disease in tomato and chilli with disease severity of 20 and 60 per cent, respectively.

Study on host range of A. solani (AS3) on different solanaceous crops. A host range of Alternaria solani was studied on solanaceous crops. About five plants in each solanaceous crops like tomato, chilli, brinjal and capsicum were screened for the symptom expression against Alternaria solani.

The results obtained are shown in the Table 1 and Plate 2. It was observed that all the solanaceous crops, which were inoculated with spore suspension of Alternaria solani (AS3) exhibited the early blight symptoms. The more and early symptoms were exhibited in tomato plants with maximum PDI of about 8.51 per cent after 7 days of inoculation. Though other crops expressed the disease symptoms, but PDI was very less. PDI in capsicum was about 3.25 per cent and in chilli 1.30 per cent, which were expressed after 12 and 13 days of inoculation of pathogen, respectively. However, very low early blight symptoms were expressed in brinjal leaves with PDI of 0.22 per cent at 15 days after pathogen inoculation was documented.

This investigation was supported by Tsedaley (2014) and reported that an early blight of potato was prevalent across worldwide, wherever potatoes, tomatoes, peppers and eggplants were grown. Cardoso (2014) conducted pathogenicity tests on 28 species of solanaceae, among them thirteen solanaceous crop species were found susceptible to Alternaria solani.

Table 1: Host range study of Alternaria solani (AS3) on different solanaceous crops.

Plate 2. Host range study of Alternaria solani (AS3) on solanaceous crops.

Screening of potato germplasms against early blight disease. The results related to both the field and polyhouse screening of potato genotypes were presented in Table 2 & Plate 3. Among twenty genotypes screened, none of them showed immune response. Only seven genotypes were gave resistant reaction viz., CP-3352, CP-3377, CP-3376, CP-3318, CP-3337, CP-3322 and CP-3175. Whereas, six genotypes were showed moderately resistant viz., CP-3393, CP-3421, CP-3382, CP-3325, CP-3421 and CP-3210. But, four genotypes were indicated moderately susceptible viz., CP-3420, CP-3083, CP-3415 and CP-3361. Whereas, three genotypes were showed susceptible reaction viz., CP-3395, CP-3112 and CP-3397. However, none of the genotypes were found to be highly susceptible. 

Kumar et al. (2015) reported that cultivars KDTS-71, DVRT-1-2, CO-3, PANT-T-3 and VFN-8 were found to be highly resistant to early blight in field screening as well as polyhouse conditions. A similar attempts were made by Ghani and Ganie (2013) who reported that, three genotypes viz., Kufri Himalini, SM/96-27 and SM/94-44 were moderately tolerant. Whereas, nine genotypes viz., Kufri Giridari, Kufri Shailaja, Kufri Chandramukhi, SM/98-239, SM/93-237, SM/90-45, HB/82-18, HB/50-45 and Shalimar potato-1 were moderately susceptible. Mehboob et al. (2013) reported that FD-18 potato was found to be resistant. Whereas, two lines such as F3-39 and FD-48-41 were showed moderately resistant response to early blight disease of potato.

Table 2: Screening of potato germplasms against early blight disease.

Plate 3. Potato germplasms screening under natural condition.

A roving survey was carried out to know the status of early blight diseases severity in Southern Karnataka. The severity of early blight was found higher in Mulabagilu taluk with disease severity of 29.92 per cent followed by Kolar (21.60%) and Shidlaghatta (20.52%) of Kolar and Chikkballapura districts, respectively. Host range studies of solanaceous crops revealed that, more and early symptoms were exhibited in tomato plants with maximum PDI of about 8.51 per cent after 7 days of inoculation. Among the twenty genotypes screened, no genotypes were showed immune response to early blight disease. Only seven genotypes indicated resistant reaction viz., CP-3352, CP-3377, CP-3376, CP-3318, CP-3337, CP-3322 and CP-3175. Whereas, three genotypes were showed susceptible reaction viz., CP-3395, CP-3112 and CP-3397 and none of the genotypes were found to be highly susceptible. Hence, some of resistant and moderately resistant germplasms can be exploited in the breeding programme and recommended to the farming community as resistant sources for effective management of early blight disease of potato.

To study of Alternaria species complexity in potato and studies on molecular variability of different isolates of Alternaria solani.  

Manjamma D., Prasad P.S., H. Amarananjundeswara, Manjunath Hubballi and  Chandrashekhar G.S.  (2024). Survey, Host Range studies and Germplasm Screening Against Early Blight Disease of Potato caused by Alternaria solani. Biological Forum – An International Journal, 16(10): 130-134.