Tree species in the arid and semi-arid regions use various strategies to combat drought stress. Ziziphus nummularia, native to the Thar Desert in India, is highly drought-tolerant. To identify the most drought-tolerant ecotype of Z. nummularia, one ecotype each from semi-arid (Godhra, annual rainfall > 750 mm), arid (Bikaner, 250–350 mm) and hyper-arid (Jaisalmer, < 150 mm) regions was selected along with two other Ziziphus species; Z. mauritiana and Z. rotundifolia, and screened for parameters contributing to drought tolerance. Among these, Z. nummularia (Jaisalmer) (CIAHZN-J) was the most drought-tolerant. The tolerance nature of CIAHZN-J was associated with increased membrane stability, root length and number, length of hairs and thorns, root dry/fresh weight ratio, seed germination (at −0.5 MPa), proline content (31 fold), catalase and sugar content (2 to 3 fold). Apart from these characteristics, it also exhibited the longest duration to reach highest cumulative drought stress rating, maintained higher relative water content for a longer period of time with reduced leaf size, leaf rolling and falling of older leaves, and displayed sustained shoot growth during drought stress. To determine drought tolerance in Ziziphus, we developed a morphological symptom-based screening technique in this study. Additionally, transcriptome profiling of CIAHZN-J in response to drought revealed the up-regulation of genes involved in sugar metabolism and transport, ABA biosynthesis, osmo-regulation, ROS homeostasis and maintaining water potential. Expression profiles and semi-quantitative reverse transcription PCR results further correlated with the physiological and biochemical mechanisms. In conclusion, CIAHZN-J is an excellent genetic stock for the identification of drought-responsive genes and can also be deployed in crop improvement programmes for drought tolerance.
Intensive cultivation, climate change and host–pathogen dynamics/interaction had led to emergence of viral diseases and vector population, thereby causing significant economic losses. In the present study, extensive surveys were conducted (during 2016–2017) followed with field experiments (2017 and 2019 kharif and 2018 rabi seasons) in the state of Chhattisgarh, India, comprising of three diverse agroecological zones, viz., northern hill zone, central plain zone and southern Bastar plateau zone, for understanding the distribution pattern of viruses and vector populations in prominent pulses and vegetable crops. Field experiments revealed that more than 90% incidence of yellow mosaic disease (YMD) was recorded in mungbean and urdbean, followed by YMD of ridge gourd and bitter gourd, leaf curl disease of tomato (ToLCD) and chilli and yellow vein mosaic disease of bhendi; however, only five per cent YMD was recorded in cow pea. Molecular and sequence analysis of viral genomic components revealed ToLCD in central plain zone of Chhattisgarh was caused by a consortium of begomoviruses, including Tomato leaf curl New Delhi virus (ToLCNDV), Tomato leaf curl Karnataka virus (ToLCKV), and Tomato leaf curl Kerala virus associated with satellite molecules. YMD of mungbean, cow pea and soybean was caused by Mungbean yellow mosaic India virus (MYMIV), while YMD of ridge gourd was caused by ToLCNDV. PCR analysis, using species‐specific primers, of samples representing the three different regions revealed that YMD of mungbean, urdbean and cowpea was positive only for MYMIV and was unevenly distributed, while YMD of ridge gourd, bitter gourd, pumpkin and sponge gourd was positive only for ToLCNDV; however, ToLCD was positive for either ToLCNDV or ToLCKV or both, and some samples were also found associated with betasatellite molecules. Amaranthus and rice bean were identified as non‐host species for the begomoviruses infecting tomato and MYMIV, as observed by surveys in the hot‐spot‐like areas, controlled whitefly transmission as well as agroinoculation. Compilation and analysis of available information on begomoviruses affecting these crops in India suggest that they are unevenly distributed in India. This is the first report of the begomovirus occurrence in pulses and vegetable crops in this agroecologically diverse region.
Yellow mosaic disease of Cajanus scarabaeoides (L.) Thouars (CsYMD) was observed in up to 46% of C. scarabaeoides plants in the mungbean, urdbean and pigeon pea fields from 22 districts of Chhattisgarh State, India, during 2017-2019. The symptoms were characterized by yellow mosaic on green leaves and yellow discoloration of leaves in advanced stages of the disease. Severely infected plants showed shortened internodal length and reduced leaf size. CsYMD was transmissible to healthy C. scarabaeoides and Cajanus cajan by whitefly (Bemisia tabaci). The plants thus infected developed typical yellow mosaic symptoms on their leaves within 16 and 22 days of inoculation, respectively, suggesting a begomovirus etiology. Molecular analysis revealed that this begomovirus has a bipartite genome composed of DNA-A (2729 nucleotides) and DNA-B (2630 nucleotides). Sequence and phylogenetic analyses revealed that the nucleotide sequence of the DNA-A component had the highest identity of 81.1% with DNA-A of Rhynchosia yellow mosaic virus (RhYMV) (NC_038885) followed by mungbean yellow mosaic virus (MN602427) (75.3%). DNA-B had the highest identity of 74.0% with DNA-B of RhYMV (NC_038886). As per ICTV guidelines, this isolate had <91% nucleotide identity with DNA-A of any of the begomoviruses reported, hence, it is proposed as a new begomovirus species, tentatively named Cajanus scarabaeoides yellow mosaic virus (CsYMV). After agroinoculation with DNA-A and DNA-B clones of CsYMV, all Nicotiana benthamiana plants developed leaf curl symptoms along with light yellowing symptoms 8-10 days after inoculation (DAI), while ~60% of the C. scarabaeoides plants developed yellow mosaic symptoms similar to those observed in the field 18 DAI, thus fulfilling the Koch’s postulates. From these agro-infected C. scarabaeoides plants, CsYMV was transmissible to healthy C. scarabaeoides plants by B. tabaci. Apart from these hosts, CsYMV also infected and caused symptoms in mungbean and pigeon pea.
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