A new collar rot disease of cowpea (Vigna unguiculata) caused by Aplosporella hesperidica in India

Comparative Analysis of the Expression of Resistance-Related Genes Respond to the Diversity Foliar Pathogens of Pseudostellaria heterophylla

The foliar disease, which is the primary complex disease of Pseudostellaria heterophylla, can be caused by multiple co-infecting pathogens, resulting in a significant reduction in yield. However, there is a lack of research on the relationship between co-infection of various pathogens and the response of resistance-related genes in P. heterophylla. Through the use of 18S rDNA sequencing and pathogenicity testing, it has been determined that Fusarium oxysporum, Alternaria alternata, Arcopilus aureus, Botrytis cinerea, Nemania diffusa, Whalleya microplaca, and Cladosporium cladosporioides are co-infecting pathogens responsible for foliar diseases in P. heterophylla. Furthermore, the qRT-PCR analysis revealed that F. oxysporum, A. alternata, B. cinerea, A. aureus, N. diffusa, Schizophyllum commune, C. cladosporioides, and Coprinellus xanthothrix upregulated ten, two, three, four, seven, thirteen, five, one, and six resistance-related genes, respectively. These findings suggest that a total of 22 resistance-related genes were implicated in the response to diverse fungi, and the magnitude and frequency of induction of resistance-related genes varied considerably among the different fungi. The aforementioned gene associated with resistance was found to be implicated in the response to multiple fungi, including PhPRP1, PhBDRN15, PhBDRN11, and PhBDRN3, which were found to be involved in the resistance response to nine, five, four, and four fungi, respectively. The findings indicate that the PhPRP1, PhBDRN15, PhBDRN11, and PhBDRN3 genes exhibit a broad-spectrum resistance to various fungi. Furthermore, the avirulence fungi C. xanthothrix, which is known to affect P. heterophylla, was found to prime a wide range of resistance responses in P. heterophylla, thereby enhancing its disease resistance. This study provided insight into the management strategies for foliar diseases of P. heterophylla and new genetic materials for disease-resistant breeding.

Re-Evaluating Botryosphaeriales: Ancestral State Reconstructions of Selected Characters and Evolution of Nutritional Modes

Botryosphaeriales (Dothideomycetes, Ascomycota) occur in a wide range of habitats as endophytes, saprobes, and pathogens. The order Botryosphaeriales has not been subjected to evaluation since 2019 by Phillips and co-authors using phylogenetic and evolutionary analyses. Subsequently, many studies introduced novel taxa into the order and revised several families separately. In addition, no ancestral character studies have been conducted for this order. Therefore, in this study, we re-evaluated the character evolution and taxonomic placements of Botryosphaeriales species based on ancestral character evolution, divergence time estimation, and phylogenetic relationships, including all the novel taxa that have been introduced so far. Maximum likelihood, maximum parsimony, and Bayesian inference analyses were conducted on a combined LSU and ITS sequence alignment. Ancestral state reconstruction was carried out for conidial colour, septation, and nutritional mode. Divergence times estimates revealed that Botryosphaeriales originated around 109 Mya in the early epoch of the Cretaceous period. All six families in Botryosphaeriales evolved in the late epoch of the Cretaceous period (66-100 Mya), during which Angiosperms also appeared, rapidly diversified and became dominant on land. Families of Botryosphaeriales diversified during the Paleogene and Neogene periods in the Cenozoic era. The order comprises the families Aplosporellaceae, Botryosphaeriaceae, Melanopsaceae, Phyllostictaceae, Planistromellaceae and Saccharataceae. Furthermore, current study assessed two hypotheses; the first one being "All Botryosphaeriales species originated as endophytes and then switched into saprobes when their hosts died or into pathogens when their hosts were under stress"; the second hypothesis states that "There is a link between the conidial colour and nutritional mode in botryosphaerialean taxa". Ancestral state reconstruction and nutritional mode analyses revealed a pathogenic/saprobic nutritional mode as the ancestral character. However, we could not provide strong evidence for the first hypothesis mainly due to the significantly low number of studies reporting the endophytic botryosphaerialean taxa. Results also showed that hyaline and aseptate conidia were ancestral characters in Botryosphaeriales and supported the relationship between conidial pigmentation and the pathogenicity of Botryosphaeriales species.

Constraints and Prospects of Improving Cowpea Productivity to Ensure Food, Nutritional Security and Environmental Sustainability

Providing safe and secure food for an increasing number of people globally is challenging. Coping with such a human population by merely applying the conventional agricultural production system has not proved to be agro-ecologically friendly; nor is it sustainable. Cowpea (Vigna unguiculata (L) Walp) is a multi-purpose legume. It consists of high-quality protein for human consumption, and it is rich in protein for livestock fodder. It enriches the soil in that it recycles nutrients through the fixation of nitrogen in association with nodulating bacteria. However, the productivity of this multi-functional, indigenous legume that is of great value to African smallholder farmers and the rural populace, and also to urban consumers and entrepreneurs, is limited. Because cowpea is of strategic importance in Africa, there is a need to improve on its productivity. Such endeavors in Africa are wrought with challenges that include drought, salinity, the excessive demand among farmers for synthetic chemicals, the repercussions of climate change, declining soil nutrients, microbial infestations, pest issues, and so forth. Nevertheless, giant strides have already been made and there have already been improvements in adopting sustainable and smart biotechnological approaches that are favorably influencing the production costs of cowpea and its availability. As such, the prospects for a leap in cowpea productivity in Africa and in the enhancement of its genetic gain are good. Potential and viable means for overcoming some of the above-mentioned production constraints would be to focus on the key cowpea producer nations in Africa and to encourage them to embrace biotechnological techniques in an integrated approach to enhance for sustainable productivity. This review highlights the spectrum of constraints that limit the cowpea yield, but looks ahead of the constraints and seeks a way forward to improve cowpea productivity in Africa. More importantly, this review investigates applications and insights concerning mechanisms of action for implementing eco-friendly biotechnological techniques, such as the deployment of bio inoculants, applying climate-smart agricultural (CSA) practices, agricultural conservation techniques, and multi-omics smart technology in the spheres of genomics, transcriptomics, proteomics, and metabolomics, for improving cowpea yields and productivity to achieve sustainable agro-ecosystems, and ensuring their stability.

Dactuliophora mysorensis sp. nov.: A New Species of Mycelia Sterilia Causing Zonate Leaf Spot on Cowpea in India

Cowpea is an important pulse crop extensively grown in arid and semi-arid tropics which is affected by a number of diseases. Fungi belonging to mycelia sterilia are known to cause many diseases on cereals and pulses. During the cowpea field survey in Mysore District of Karnataka (India), Dactuliophora sp. was identified as the major pathogen causing zonate leaf spot (ZLS) disease. The fungal pathogen was isolated from naturally infected cowpea leaves and identified as a member belongs to the genus Dactuliophora, which was previously described by CLA Leakey in the year 1964 on Vigna unguiculata from Africa. However, detailed morphological and cultural examinations of the pathogen revealed striking differences from that of D. tarrii. Based on differences in morphology with D. tarrii, a new species Dactuliophora mysorensis sp. nov. is described herein. The disease incidence as well as disease index was estimated for 3 years (2016-2018). The severity of the disease was high during August-November. High incidence and disease index of ZLS was recorded in Doddamaragowdanahally region. The pathogenicity tests demonstrated similar symptoms of ZLS. The ITS barcoding revealed that the pathogen is closely related to Rhizoctonia bataticola and Macrophomina phaseolina. Further, in vitro evaluation of fungicides was carried out by poisoned food technique. Among the five fungicides examined, only two systemic fungicides (Benomyl and Carbendazim) were effective against D. mysorensis. Thus, the present study recommends Benomyl and Carbendazim for management of ZLS disease caused by D. mysorensis.

First Report of Nigrospora sphaerica associated with Leaf Spot Disease of Cowpea (Vigna unguiculata) from India

Cowpea (Vigna unguiculata (L.) Walp) is one of the main legume crops grown in arid and semi-arid regions in the world. Brazil, Haiti, Myanmar, Nigeria, Sri Lanka, United States, and India contributes to the substantial production of cowpea at the global level (Mahadevakumar and Janardhana, 2012, 2014). Field surveys conducted during 2017-19 (August-September) in major cowpea growing regions of southern Karnataka revealed the occurrence of characteristic leaf spot disease of unknown etiology with an incidence ranging from 6 to 8%. Initially, the symptoms developed as small specks (1.5 to 3.5 mm), characterized by circular or irregular shape. These lesions began to develop from the leaf margin and regularly extended and coalesced to form larger lesions. After the successful manifestation of the symptoms on leaves, the associated fungal pathogen was isolated. In brief, the infected leaves were surface sterilized with 2% NaOCl for 2 min, rinsed thrice in sterile distilled water (SDW) and blotter dried. The leaf sections were placed on potato dextrose agar (PDA) in Petri plates and incubated at room temperature (27 ± 2°C) for 10 to 12 days. Mycelia developed from infected tissues were transferred to fresh PDA plates and pure cultures were obtained. Mycelia were initially white and eventually turned into gray. The conidia were black, single-celled, smooth, spherical to subspherical, 10 to 22 μm in diameter (n=30), and borne singly on a hyaline vesicle at the tip of each conidiophore. Based on the cultural features and conidial morphology, the fungus was identified as Nigrospora sp. Further, to identify the pathogen to the species level, the ITS region of the ribosomal RNA gene was amplified using primers ITS1 and ITS4 (White et al. 1990). The amplified PCR products were purified and sequenced. The nBLAST analysis showed 100% similarity with reference sequences from the GenBank database Nigrospora sphaerica (MT225783.1; MN795578.1), and the sequences were deposited in GenBank (Accession No. MT305812.1, MT305813.1, MT305814.1). Based on the cultural, morphological, microscopic and molecular characteristics, the associated fungal pathogen was identified as N. sphaerica (Sacc.) Mason (Chen et al. 2018; Wang et al. 2017) and a voucher specimen was deposited at University of Mysore Herbarium with accession No. UOM20-NS1. Further, pathogenicity tests were conducted on healthy cowpea plants grown under greenhouse conditions. Inoculations were made with conidial suspension (105 conidia/ml) prepared in SDW and healthy plants sprayed with SDW served as a standard control. All the plants were covered with polyethylene bags for 24-48 hr and observations were made at regular intervals. Typical necrotic lesions developed after 12 days of inoculation and no such symptoms were observed on the standard control set. The associated pathogen was re-isolated from diseased leaves and its identity confirmed based on morphology and cultural characteristics. Leaf spots are becoming a major problem in cowpea growing areas in recent years (Dactuliophora sp., Pestalotiopsis leaf spot, Alternaria leaf spot, and many others) (Mahadevakumar and Janardhana 2012, 2014). Recently, Aplosporella hesperidica causing collar rot on cowpea has been reported from the same region (Deepika et al. 2020). The seed borne occurrence N. sphaerica on cowpea is reported from Brazil (Rodrigues and Menezes 2002), there are no previous reports available on the occurrence of N. sphaerica on cowpea leaf spots, the present investigation is the first report of N. sphaerica causing leaf spot disease on cowpea from India.