First Report of <i>Fusarium solani</i> associated with root rot of Kiwifruit ( <i>Actinidia deliciosa</i> Chevalier) in India

Kiwifruit (Actinidia deliciosa Chevalier), recently introduced as a potential cash crop in India, covers an area of about 5000 ha with production of 18,000 MT of fruits (MoAFW, 2023-24). Symptoms of crown and root rot, wilting, and poor fruit quality were observed in kiwifruit plants at an orchard in Kashmir, Shalimar, India (34.146ºN and 74.881ºE). The disease incidence varied from 22.86% in first year to 25.20% in second year with an average disease incidence of 24.03% during the study years. Fungal colonies were isolated from root samples of 12 symptomatic plants maintained at SKUAST-K, Shalimar, India. The fungal colonies were sub-cultured and purified by single spore method. The colony morphology with the highest isolation frequency of 55.55% was further examined. The fungus was named as KFRR1 with n=10 isolates (KFRR1-KFRR10). The colony grown on Potato dextrose agar (PDA) with alternating 12-h-light/12-h-dark cycles, exhibited white coloured smooth mycelial growth with slight purplish tinge after 7 days of incubation. It produced concentric rings with creamy yellow exudates after 10 days of incubation at 25±2°C. The reverse side exhibited orange pigmentation. The mycelium was hyaline, branched, septate and 3.40-5.10µm in diameter. Macroconidia were hyaline, fusiform to moderately curved, 3–4-septate and measured 20.50–32.00µm × 3.40–4.50µm (mean 26.50 × 3.95µm). Microconidia were hyaline, cylindrical to oval, 0–1-septate, and measured 7.40–10.30µm × 2.70–3.75µm (mean 8.85 × 3.22µm). The chlamydospores were hyaline, in chains and globose to round in shape and measured 4.8-8.4µm long (mean 6.6µm) and 7.5-8.8µm wide (mean 8.1µm). Morpho-cultural characterization supported the identification of the isolate KFRR1 as Fusarium spp. DNA bar-coding was used to characterize isolate KFRR1 at the molecular level, using three regions: Internal transcribed spacer (ITS), elongation factor (EF-1α) and beta-tubulin (β-tub) (White et al. 1990; O’Donnell et al. 2008). The ITS and EF-1α sequence of KFRR1 showed 100% and 99% similarity with F. solani NRRL 54981 (KC808246, KC808204) respectively and β-tub sequence showed 99% similarity with F. solani BCCM/IHEM:2099 (KJ125995). The sequences were deposited in GenBank under accession numbers: PQ721622 (ITS), PV007955 (β˗tub) and PV054449 (EF 1α). Maximum likelihood phylogeny with 1000 bootstrap replicates, grouped KFRR1 with Fusarium solani for all three genes (Tamura et al., 2013). Pathogenicity test was conducted on Kiwifruit seedlings (Hayward variety) by the pin prick method (Polat et al. 2017). Symptoms first appeared on Kiwifruit plants 66 days after inoculation, and the plants inoculated with isolates of Fusarium solani died 72 days after inoculation. Both above and below ground symptoms were similar to the symptoms observed in the field. Control plants remained healthy. The pathogen was re-isolated on PDA and resembled with morpho-molecular characters of F. solani to satisfy the Koch’s postulates. This pathogen is reported to cause root rot in Kiwifruit in China (Song et al. 2023). To our knowledge, this is the first report of F. solani causing root rot of kiwifruit in India and highlights the need of proper diagnosis of the causal pathogen before management schedule of this new crop can be devised.