First report of Cotton leaf curl Multan virus infecting Millettia pinnata in Pakistan

Abstract

Millettia pinnata (Pongame oiltree, Sukh chain; family Fabaceae) is an important leguminous tree widely grown and utilised as a herb in Southeast Asia and the Indian subcontinent. In October 2020, symptoms of stunted growth, leaf curling (upward and downward) and vein thickening (Figures 1 and 2), which are associated with infection by Begomovirus species in other hosts, were observed on M. pinnata, growing near cotton fields (30.3°N, 73.0°E), in Faisalabad, Punjab Province, Pakistan. DNA was isolated from ten leaves (S1 to S10), one each from ten diseased plants, and one leaf from two asymptomatic plants (AS11 and AS12) using a cetyl trimethyl ammonium bromide protocol (Doyle & Doyle, 1990). Rolling circle amplification in combination with PCR using begomovirus universal primers (BegomoF/BegomoR) (Briddon & Markham, 1994) amplified a c. 2.8 kb product from all the diseased samples. PCR assays for the Begomovirus alphasatellite (primer pair DNA101F/DNA101R) (Bull et al., 2003) and betasatellite (primer pair Beta01F/Beta02F) (Briddon et al., 2002) each amplified a c. 1.4 kb product from all the diseased samples. Neither begomovirus genome nor satellite DNA was detected in the asymptomatic samples. Amplicons from the begomovirus genome (AV-2 and AV-3 from S1 and S2; MZ268122-MZ268123), alphasatellite (AV-36 from S1; MZ057253) and betasatellite (AV-8 and AV-10 from S1, AV-11 and AV-12 from S2, and AV-13 from S3; MZ057231- MZ057235), were cloned in a general purpose PTZ57R/T cloning vector (Thermo Fisher Scientific, USA), Sanger sequenced, and the sequences deposited in GenBank. The genome sequences shared >99% nucleotide identity with Cotton leaf curl Multan virus (CLCuMuV) and were most closely related to CLCuMuV strain NAS-14 (MK357257), which was found in cotton in the same region of Faisalabad (Ahmed et al., 2021). They also had 94% and 87% nt similarity with the CLCuMuV-Raj (AF363011) and CLCuMuV-Dar strains (EU365613) respectively. Moreover, the alphasatellite and betasatellite sequences shared 98% similarity with Cotton leaf curl Multan alphasatellite (CLCuMuA; MK357286.1) and betasatellite (CLCuMuB; MT920327.1), respectively. The five CLCuMuB betasatellite sequences (MZ057231-MZ057235) shared 99% identity and the two Begomovirus genomic sequences (MZ268122-MZ268123) from the M. pinnata samples had 99% identity with each other. Southern hybridization (Zubair et al., 2017) confirmed the detection of Begomovirus genomic DNA and quantitative real-time PCR (Shafiq et al., 2017) assays confirmed the detection of CLCuMuV in three samples, S1, S2 and S3, selected for further analysis. To the best of our knowledge, this is the first report of CLCuMuV in Millettia pinnata which may serve as an alternative host of the virus in the off season when cotton is not grown. Routine monitoring and detection of CLCuMuV is essential to prevent the devastating leaf curl disease it causes from spreading worldwide. The authors acknowledge support in Sanger sequencing from Dr. Brian Scheffler and his group from USDA-ARS.