Prashant Prakash Jambhulkar

As environmental and health concerns increase, the trend toward sustainable agriculture is moving toward using biological agents. About 60% of all biological fungicides have Trichoderma species as the active ingredient, with T. harzianum as the most common species in these products. However, the name T. harzianum has often been used incorrectly in culture collections, databases, and scientific literature due to the division of the Harzianum clade (HC) into more than 95 cryptic species, with only one being named T. harzianum. In this study, 49 strains previously identified as T. harzianum in three surveys of Trichoderma species from soils in South and Central America were re-identified using phylogenetic analyses based on tef1α, rpb2, and ITS sequences obtained from GenBank. These were combined with the HC species from two other studies, which were identified based on the current taxonomy. Based on the results of the five surveys of the total 148 strains in HC, 11 species were identified. T. afroharzianum, T. lentiforme, and T. endophyticum, followed by T. azevedoi and T. harzianum, were the dominant species of the HC in South and Central America. This is the first report to identify dominant Trichoderma species within the HC in South and Central American soil based on multiple studies. These results will be useful in selecting strains within the clade for the formulation of biocontrol and biofertilizer products on the continent.

As environmental and health concerns increase, the trend of sustainable agriculture moves toward using biological agents. About 60% of all biological fungicides have Trichoderma species as the active ingredient, with T. harzianum as the most common species in these products. However, the name T. harzianum has often been incorrectly used in culture collections, databases, and the scientific literature due to the division of the Harzianum Complex Clade (HCC) into more than 95 cryptic species with only one being named T. harzianum. In this study, 49 strains previously identified as T. harzianum in three surveys of Trichoderma species from soils in South and Central America were re-identified using phylogenetic analyses based on tef1α, rpb2, and ITS loci and were combined with the corresponding species in two other studies, where the species were correctly identified. Based on the results of the five surveys of the total 148 strains in HCC, 11 species were identified and T. afroharzianum, T. lentiforme, T. endophyticum followed by T. azedevio and T. harzianum were detected as the dominant species of the HCC in South and Central America. This is the first report of identifying dominant Trichoderma species within the HCC in South and Central American soil based on multiple studies, which will be useful in selecting strains within the complex clade for formulation of biocontrol and biofertilizer products in the continent.

Fusarium stalk rot (FSR), caused by the Fusarium species complex, is an economic threat to maize cultivation all over the world. We investigated the population structure and genetic diversity of Fusarium species obtained from five major maize-growing regions in India. The Tef-1α locus was used for phylogenetic analysis of geographically distinct isolates of Fusarium verticillioides, F. andiyazi, F. proliferatum, F. nygamai, and F. acutatum causing FSR. A phylogenetic tree showed monophyletic, polyphyletic, and paraphyletic groupings reflecting the complex evolutionary history and genetic diversity within the genus. Monophyletic groupings depicting strong bootstrap support were shown to have a single common ancestor and genetic coherence with limited genetic divergence among sequences. Polyphyletic groupings also presented significant genetic differentiation within the F. verticillioides sequences from diverse ecological niches. Nucleotide diversity of moderate level 0.02471 reflected genetic variations within populations that were attributed to factors such as mutation, genetic drift, or varying selection pressures. The Fst value of 0.98205 is particularly indicative of high genetic differentiation, implying that most of the genetic variance is due to differences between populations rather than within them. F. verticillioides, with 57 sequences, showed low genetic diversity with three segregating sites and a low haplotype diversity of 0.19486, suggesting the founder effect, where a reduced population expands from a limited genetic pool. The total data estimates across all populations for haplotype analysis showed 72 sequences, 44 segregating sites, and 9 haplotypes with a haplotype diversity of 0.48513. The evolutionary dynamics showed genetic differentiations among Fusarium species causing FSR. AMOVA indicated high within-population variations, depicting a substantial genetic diversity within individual populations. The results offer a comprehensive framework for discussing the implications of genetic diversity in pathogen management and the evolutionary dynamics of the Fusarium species causing FSR in maize in the Indian subcontinent.

As environmental and health concerns increase, the trend of sustainable agriculture moves toward using biological agents. About 60% of all biological fungicides have Trichoderma species as the active ingredient, with T. harzianum as the most common species in these products. However, the name T. harzianum has often been incorrectly used in culture collections, databases, and the scientific literature due to the division of the Harzianum Complex Clade (HCC) into more than 95 cryptic species with only one being named T. harzianum. In this study, strains previously identified as T. harzianum in three surveys of Trichoderma species from soils in South and Central America were reanalyzed using phylogeny based on tef1α, rpb2, and ITS loci and combined with the corresponding species in two other studies, where the species were correctly identified. Based on the results of the five surveys, T. afroharzianum, T. lentiforme, T. endophyticum followed by T. azedevio and T. harzianum were found to be the dominant species of the HCC in South and Central America. This is the first report of identifying dominant Trichoderma species within the HCC in South and Central American soil based on multiple studies, which will be useful in selecting strains within the complex clade for formulation of biocontrol and biofertilizer products in the continent.

Certain Trichoderma isolates provide biofertilizer, biocontrol, and other plant-beneficial activities while inhabiting the soil or internal plant tissue, and their use in agricultural systems can contribute to sustainable food production. It is thought that colonization of soil or internal plant tissue is fundamental for biocontrol and biofertilizer applications. Our collective analyses of prior surveys, where the tef1α sequence was almost exclusively used to identify Trichoderma species, showed that isolates from the Harzianum complex clade, the T. asperellum/T. asperelloides group, T. virens, T. hamatum, and T. atroviride were prevalent in soil and/or as endophytes. Population structure and genetic diversity based on the genetic markers tef1α, rpb2, and ITS were investigated, and new lineages with statistical bootstrap support within T. atroviride, T. asperellum, T. hamatum, and T. virens populations were found. The nearest relatives of some of these species were also revealed. Choosing isolates from among more than 500 known Trichoderma species for use in non-targeted evaluation screens for biocontrol or biofertilizer applications is time-consuming and expensive. Preferentially selecting isolates from T. atroviride, T. asperellum/T. asperelloides, T. hamatum, the T. harzianum complex clade, T. virens, and possibly nearest relatives may speed the identification of candidates for commercialization due to the demonstrated ability of these species to successfully inhabit the soil and internal plant tissue. To our knowledge, this is the first report where dominant soil and endophytic Trichoderma species were identified from past survey data and population structure and genetic diversity analyses conducted.

Fusarium stalk rot (FSR) caused by the Fusarium species complex is an economic threat to maize cultivation all over the world. We investigated the population structure and genetic diversity of Fusarium spp. obtained from five major maize-growing regions of India. The Tef-1α locus was used for phylogenetic analysis of geographically distinct isolates of Fusarium verticillioides, F. andiyazi, F. proliferatum, F. nygamai, and F. acutatum causing FSR. Geographical separation among four local populations contributed to 7.87% variance, whereas 92.12% of the variance was within popula-tions, suggesting a predominant influence of local adaptation or stochastic events like genetic drift within populations, with geographical separation playing a lesser but significant role in shaping genetic diversity. Genetic differentiation statistics between Fusarium species showed lower gene flow from haplotypes except in the population of F. acutatum and F. andiyazi having high GST values. In contrast, a high Kxy was reported, indicating elevated genetic differentiation between populations. The haplotype network analysis revealed the presence of eight distinct haplotypes which reflected pathogenic evolution and adaptive potential of Fusarium spp. The results offer a comprehensive framework for discussing the implications of genetic diversity in pathogen management and the evolutionary dynamics of the Fusarium spp. causing FSR of maize in the Indian subcontinent.

There are fewer studies on Trichoderma diversity in agricultural fields. The rhizosphere of 16 crops was analyzed for Trichoderma species in 7 districts of Rajasthan state of India. Based on DNA sequence of translation elongation factor 1α (tef-1α), and morphological characteristics, 60 isolates were identified as 11 species: Trichoderma brevicompactum, species in Harzianum clade identified as T. afroharzianum, T. inhamatum, T. lentiforme, T. camerunense, T. asperellum, T. asperelloides, T. erinaceum, T. atroviride, T. ghanense, and T. longibrachiatum. T. brevicompactum is the most commonly occurring strain followed by T. afroharzianum. No new species were described in this study. T. lentiforme, showed its first occurrence outside the South American continent. The morphological and cultural characteristics of the major species were observed, described, and illustrated in detail. The isolates were tested for their antagonistic effect against three soilborne plant pathogens fungi: Sclerotium rolfsii, Rhizoctonia solani, and Fusarium verticillioides in plate culture assays. One of the most potent strains was T. afroharzianum BThr29 having a maximum in vitro inhibition of S. rolfsii (76.6%), R. solani (84.8%), and F. verticillioides (85.7%). The potential strain T. afroharzianum BThr29 was also found to be efficient antagonists against soil borne pathogens in in vivo experiment. Such information on crop selectivity, antagonistic properties, and geographic distribution of Trichoderma species will be beneficial for developing efficient Trichoderma-based biocontrol agents.

Maize (Zea mays) is the most influential crop in the world, which can grow in temperate as well as tropical conditions. It is a major source for food, livestock, the beverage industry and cosmetics. In recent days maize production decreased drastically due to many diseases. Fusarium stalk rot is one among them. To evaluate the genotypes resistance against PFSR, 40 maize genotypes were subjected against five virulent isolates of Fusarium using the same artificial inoculation method. Varying disease reactions among the inbreds, with some exhibiting premature drying and lodging. After 40 days post-inoculation, internode infection was observed, and disease severity was assessed based on lesion spread within or across internodes. The inbreds were categorized according to their resistance levels, ranging from highly resistant to highly susceptible based on internode infection. Only one inbred showed high resistance to both FUR11 and Raichur isolates. None of the inbreds exhibited high resistance or resistance against the F1 isolate. Eight inbreds showed resistance against multiple isolates. One inbred, DML-1802, displayed high resistance to FUR11 and resistance to Raichur isolate, while another, A8-6, was highly susceptible to all tested isolates, showing infection spreading up to two internodes and observed xylem vessel rotting and hollow stems. Eleven resistant inbreds against Fusarium stalk rot were selected for a breeding program aimed at developing Fusarium stalk rot-resistant hybrids. The identification of variability among Fusarium species causing stalk rot in maize provided valuable insights for future research due to the limited understanding of Fusarium heterogeneity in maize stalk rot.