Ruchi Agarrwal

In March 2022, cankers and lesions appeared on the branches of 2–3-year-old pomegranate plants grown in four orchards of Hanumangarh, Rajasthan, India. The disease incidence ranged from 5-15%. Fiel...

Fungal pathogens are a major constraint affecting the quality of pomegranate production around the world. Among them, Alternaria and Colletotrichum species cause leaf spot, fruit spot or heart rot (black rot), and fruit rot (anthracnose) or calyx end rot, respectively. Accurate identification of disease-causing fungal species is essential for developing suitable management practices. Therefore, characterization of Alternaria and Colletotrichum isolates representing different geographical regions, predominantly Maharashtra—the Indian hub of pomegranate production and export—was carried out. Fungal isolates could not be identified based on morphological characteristics alone, hence were subjected to multi-gene phylogeny for their accurate identification. Based on a maximum likelihood phylogenetic tree, Alternaria isolates were identified as within the A. alternata species complex and as A. burnsii, while Colletotrichum isolates showed genetic closeness to various species within the C. gloeosporioides species complex. Thus, the current study reports for the first time that, in India, the fruit rots of pomegranate are caused by multiple species and not a single species of Alternaria and Colletotrichum alone. Since different species have different epidemiology and sensitivity toward the commercially available and routinely applied fungicides, the precise knowledge of the diverse species infecting pomegranate, as provided by the current study, is the first step towards devising better management strategies.

With increasing human global population, increased yield under saline conditions is a desirable trait for major food crops. Use of endophytes, isolated from halophytic hosts, seems to be an exciting approach for conferring salt tolerance to a salt-sensitive crop. Therefore, in the current study, fungal endophytes were isolated from halophytic plants’ roots and their ability to withstand in vitro salt stress was evaluated. The fungal endophytes could withstand up to 1M NaCl concentrations and this tolerance was independent of their host or tissue source. When inoculated on salt-sensitive wheat seeds/seedlings, several of the endophytes showed a positive impact on germination and biomass-related parameters upon salt stress, both in vitro and under glasshouse conditions. One of the isolates from dicot plants (identified as Microsphaeropsis arundinis) could successfully colonize wheat and promote its growth under salt and no-salt conditions. Amongst the fungal isolates that are known to be natural endophytes of wheat, Chaetomium globosum was the best performing isolate and has previously been reported to be an effective biocontrol agent. Based on the results of our preliminary study, we suggest that these fungal endophytes could prove beneficial for enhancing the salt stress tolerance of wheat crop.

Background: Berseem is a highly nutritious leguminous fodder crop which is used in rotation with cereal and other fodder crops due to its beneficial effects on soil nutrients. Endophytes isolated from roots of such nutritious plants are known to promote their growth as well as that of crop it is rotated with. Methods: In the current study, screening of berseem root endophytic bacteria (REB) was carried out. Morphologically distinct colonies were evaluated for their growth promotion traits in terms of phosphate solubilization, hormone production and enzyme synthesis. Their effect on plant growth parameters was also recorded. The in vitro antifungal activity was assayed using dual culture technique. The most efficient isolate was identified based on 16s rRNA gene sequence homology and subjected to biochemical analysis. Result: All the isolates exhibited plant growth promoting traits and secreted high levels of enzymes. They showed in vitro antagonistic activities against pathogenic fungi belonging to various genera which could be due to enhanced secretion of chitinase enzyme or other bioactive molecules. The most efficient isolate was found to be Gram negative and molecularly identified as Pseudomonas fluorescens which can be used for enhanced production of berseem in future.

Xanthomonas axonopodis pv. punicae (Xap) causes bacterial blight disease in pomegranates, often leading to 60–80% economic loss. In absence of a suitable Xap-resistant variety, the near-monoculture of the susceptible variety, Bhagwa, has aggravated the problem further. In recent times, Xap has spread to different geographical regions, indicating the wide adaptability of the pathogen. Moreover, lower sensitivity of Xap towards streptocycline containing streptomycin sulphate and tetracycline sulphate (9:1) under field conditions is frequently reported. Therefore, the current study was undertaken to assess the genetic variability of Xap isolates using SSR markers, their in vitro sensitivity towards streptomycin was evaluated, and the probable molecular basis of acquired resistance was studied. Two highly diverse isolates showed extreme differences in their pathogenicity, indicating the highly evolving nature of the pathogen. Moreover, all the isolates showed less than 50% growth inhibition on media containing 1500 µg/mL streptomycin, indicating a lower level of antibiotic sensitivity. On the molecular level, 90% of the isolates showed the presence of strA-strB genes involved in streptomycin metabolism. Additionally, G to A transitions were observed in the rpsL gene in some of the isolates. The molecular data suggest that horizontal gene transfer (strAB) and/or spontaneous gene mutation (in rpsL) could be responsible for the observed lower sensitivity of Xap towards streptomycin.

Sugars as photosynthates are well known as energy providers and as building blocks of various structural components of plant cells, tissues and organs. Additionally, as a part of various sugar signaling pathways, they interact with other cellular machinery and influence many important cellular decisions in plants. Sugar signaling is further reliant on the differential distribution of sugars throughout the plant system. The distribution of sugars from source to sink tissues or within organelles of plant cells is a highly regulated process facilitated by various sugar transporters located in plasma membranes and organelle membranes, respectively. Sugar distribution, as well as signaling, is impacted during unfavorable environments such as extreme temperatures, salt, nutrient scarcity, or drought. Here, we have discussed the mechanism of sugar transport via various types of sugar transporters as well as their differential response during environmental stress exposure. The functional involvement of sugar transporters in plant's abiotic stress tolerance is also discussed. Besides, we have also highlighted the challenges in engineering sugar transporter proteins as well as the undeciphered modules associated with sugar transporters in plants. Thus, this review provides a comprehensive discussion on the role and regulation of sugar transporters during abiotic stresses and enables us to target the candidate sugar transporter(s) for crop improvement to develop climate‐resilient crops.

With increasing human global population, increased yield under saline conditions is a desirable trait for major food crops. Use of endophytes, isolated from halophytic hosts, seems to be an exciting approach for conferring salt tolerance to a salt sensitive crop. Therefore, in the current study, fungal endophytes were isolated from halophytic plants’ roots and their ability to withstand in vitro salt stress was evaluated. They could withstand upto 1M NaCl concentrations and this tolerance was independent of their host or tissue source. When inoculated on salt sensitive wheat seeds/seedlings several of the endophytes showed a positive impact on germination and biomass related parameters upon salt stress, both in vitro and under glasshouse conditions. One of the isolate from dicot plants (identified as Microsphaeropsis arundinis ) could successfully colonize wheat and promote its growth under salt and no salt conditions. Amongst the fungal isolates that are known to be natural endophytes of wheat, Chaetomium globosum was the best performing isolate which has been reported as an effective biocontrol agent earlier. Based on the results of our preliminary study, we suggest that these fungal endophytes could prove beneficial for salt stress tolerance enhancement of wheat crop.