Survey, symptomatology and disease incidence
The major disease symptoms observed in most of the fields surveyed were severe upward leaf curling with puckering, crinkling of leaves and reduced intermodal length. In few locations, other characteristic symptoms
i.e reduced leaf size, leaf distortion, blistering, stunting and smaller fruits were also observed (Table 1 and Fig 1). The characteristic field symptoms of chilli leaf curl virus were upward leaf curling, puckering, reduced leaf size with no or less number of fruits
(Senanayake et al. 2007).
The results of field survey indicated the presence of leaf curl disease in all seven
mandals of Kurnool district that were surveyed. The data collected during filed survey was presented in Table 2. Maximum leaf curl incidence of 82.2 per cent was recorded in Peddakadubur village and minimum incidence of 25.0 per cent was recorded in Nagarur village of Aspari
mandal. The
mandal wise mean incidence of leaf curl disease revealed that maximum leaf curl incidence was observed in Peddakadubur
mandal (71.1%) followed by Gonegandla (59.96%), Nandavaram (52.27%), Yemmiganur (48.03%), Aspari (44.63%), Kodumur (41.50%) and with minimum leaf curl incidence in Adoni (37.83%)
mandal of Kurnool district. Similarly, 40-70% of percent disease incidence of leaf curl was recorded in Kurnool district of Andhra Pradesh
(Bagavatha devi et al. 2019).
The variation of symptomatology of plant in different
mandals indicated the presence of mixed infections of begomoviruses and infestation of sucking pests like thrips and mites. During the survey it was observed that severely affected plants produced no fruits or with significantly reduced fruits. The reasons for higher leaf curl disease incidence were continuous cultivation of chilli crop over the years (Monocropping), seasonal weather conditions which influence the sucking pest population, more number of sprayings with neonicotinoid insecticides during initial stages of crop which increases the resurgence of white fly population (vector) and non-adoption of integrated management practices. The sucking pests (whiteflies and thrips) were invariably present in all surveyed fields. Leaf curl due to sucking pest is reversible and can be managed through vector control, but leaf curl due to virus is irreversible and cannot be controlled
(Dore et al. 2017).
Information regarding chilli hybrids was collected from chilli growers during survey. It was observed that, majority of the farmers in the surveyed fields cultivated Teja, Syngenta and Deluxe hybrids (Devanur deluxe, Kohinoor deluxe, Nuziveedu deluxe and Super deluxe). Among all these, Devanur deluxe and Super deluxe were the major chilli hybrids grown in the surveyed fields. The chilli hybrids were compared based on percent disease incidence recorded during survey and found that Teja and Syngenta cultivars recorded less PDI (25.00-45.2%) of leaf curl disease compared to deluxe cultivars (30.6-82.2%) which might be due to broader leaf size of deluxe hybrids which favours sucking pest infestation, apart from tolerance levels are compared to Teja chilli hybrid.
Detection of virus and characterization of virus associated with chilli leaf curl disease
The genomic DNA was isolated from leaf samples with characteristic symptoms of begomo virus infection from Kodumur
mandal were subjected to polymerase chain reaction (PCR) using ChiLCV coat protein specific primers 5′-AGAATTATGTCCAAGCGACCA-3′ and 5′-AAGCGTTG GGGATACACAAA-3′. PCR amplification of 775 bp was observed with all isolated DNA samples. The amplified product of 775 bp was subjected to PCR purification and sequenced. The nucleotide sequence of coat protein gene (772 bp) of study isolate was deposited in GenBank and obtained accession no (MZ691516). Whenever full length sequence of begomovirus is not available, the sequence of coat protein gene serves as an effective marker in begomovirus virus identification
(Rybicki, 1994).
Different begomovirus sequences from NCBI site were used in comparative analysis. A BLAST search of GenBank revealed close sequence similarity with the Chilli leaf curl virus. The complete nucleotide sequence of coat protein gene of study isolate with other begomovirus from NCBI database revealed that it has 99.7% nucleotide similarity with chilli leaf curl virus-Guntur isolate followed by ChiLCV-Raichur isolate (Table 3) and least sequence similarity with Croton yellow vein mosaic virus (79%). In phylogeny analysis, tree forms three clusters consisting of ChiLCV and ChiLCMV (one cluster),ToLCV and ToLCNDV (Fig 2).
In India,
Khan et al (2006) reported the association of Tomato leaf curl New Delhi virus (ToLCNDV) with chilli leaf curl disease in Lucknow. Later in 2007, the association of chilli leaf curl virus with chilli leaf curl disease was reported in Jodhpur
(Senenayake et al., 2007). In the present study we confirmed the association of ChiLCV with leaf curl disease complex in Kurnool district of Andhra Pradesh.