Influence of Trichoderma spp on Macrophoma theicola branch canker disease in South Indian tea gardens, India

Branch canker disease caused by the fungus Macrophoma theicola is a major stem disease that reduces the yield of south Indian tea plantations. Hence the present study aimed to assess the efficacy of the biocontrol agent Trichoderma spp against various isolates of Macrophoma spp. For this matter, different tea-growing regions of south India were surveyed for the isolation and characterization of Macrophoma spp. Then, fungal biocontrol strains (Trichoderma viride, Trichoderma atroviride, Trichoderma harzianum, and Gliocladium virens) were procured from microbial type culture collection Centre (MTCC) to screen their antagonistic potential on different isolates Macrophoma spp. The spores of Macrophoma spp were examined through a light microscope and identified by their peculiar morphological features such as non-septum pycnidiospores present in the sac and oval shape spore with stalk and confirmed using 18S rRNA gene sequence. The results revealed that the biocontrol G. virens followed by T. harzianum showed a higher inhibitory effect on different isolates of Macrophoma spp in the dual plate and culture filtrate studies. In the well diffusion method, the fungal biocontrol agents were found to be exhibit non-significant differences on different isolates of branch canker pathogen. The hyphal interactions studies showed that the pathogenic hyphal wall shrunk and penetrated by the interaction of G. virens.

Preliminary Findings of New Citrus Rootstocks Potentially Tolerant to Foot Rot Caused by Phytophthora

Phytophthora spp. are one the most common soil-borne pathogens in citrus crops, in which Phytophthoranicotianae and P. citrophthora are the most relevant species, causing disease problems worldwide, such as foot rot and gummosis of the trunk, branch canker, brown rot of fruit, feeder root rot in orchards, and seedling damping-off in nurseries. Phytophthora-tolerant citrus rootstocks are essential for its control and for the success of the citrus industry. The aim of this study was to determine the susceptibility of new citrus rootstocks with low HLB incidence to Phytophthora diseases. Thus, plants of several commercial and new citrus rootstocks originating in different breeding programs were inoculated with an isolate of P. nicotianae. Thirty days post inoculation (DPI), the damage of lesion length in stem was measured for each plant. These results displayed a different susceptibility response to the damage caused by P. nicotianae among the citrus rootstocks tested. Thus, eleven new citrus rootstocks (B11R3T25, B11R5T25, B11R5T49, B11R5T60, B11R5T64, N40R1T18, N40R1T19, N40R3T25, WGFT + 50-7, UFR-6, and CL-5146), which have not been previously studied against Phytophthora diseases, improved the tolerance effect of Carrizo citrange. Our findings provide useful information for citrus growers on rootstock selection to address incidence problems caused by Phytophthora spp.

Cytospora and Diaporthe Species Associated With Hazelnut Canker and Dieback in Beijing, China

Hazelnut (Corylus heterophylla Fisch.) is an important nut crop in China but has been declining owing to the destructive effects of fungal branch canker and dieback. The identification and management of these pathogens are difficult because of the lack of attention to branch canker, insufficient understanding of phylogenetic, and overlapping morphological characteristics of the pathogens. In total, 51 strains were isolated from Chinese wild hazelnut in this study, and three species of Cytospora and two of Diaporthe were identified through morphological observation and multi-locus phylogenetic analyses (ITS, act, rpb2, tef1-α, and tub2 for Cytospora; ITS, cal, his3, tef1-α, and tub2 for Diaporthe). Three new species, Cytospora corylina, C. curvispora, and Diaporthe corylicola, and two known species, Cytospora leucostoma and Diaporthe eres, grew at 5–30°C and a pH of 3.0–11.0, with optimum growth at approximately 25°C and pH 4.0–7.0. Additionally, the effects of six carbon sources on mycelial growth were investigated. This study explored the main pathogenic fungi species of Corylus heterophylla, completed the corresponding database of pathogenic fungi information, and clarified their biological characteristics. Moreover, the results of this study provided a theoretical basis for Corylus heterophylla disease management and prevention in China.

Gnomoniopsis chinensis (Gnomoniaceae, Diaporthales), a new fungus causing canker of Chinese chestnut in Hebei Province, China

Chinese chestnut (Castanea mollissima) is an important crop tree species in China. However, branch canker and fruit rot are two kinds of severe diseases, which weaken the host and decrease chestnut production. During our investigations into chestnut diseases in China, several fungi have been confirmed as casual agents in previous studies, namely Aurantiosacculus castaneae, Cryphonectria neoparasitica, Cry. parasitica, Endothia chinensis and Gnomoniopsis daii. In this study, a new canker pathogen is introduced based on morphology, phylogeny and pathogenicity. Typical Gnomoniopsis canker sign of wide, orange tendrils emerging from hosts’ glaucous lenticels were obvious on the diseased trees in the field. Symptomatic branches or bark on stems from different chestnut plantations were sampled and isolated, then strains were identified by comparisons of DNA sequence data for the nuclear ribosomal internal transcribed spacer (ITS), partial translation elongation factor-1α (tef1) and β-tubulin (tub2) gene regions as well as morphological features. As a result, these strains appeared different from any known Gnomoniopsis species. Hence, we propose a novel species named Gnomoniopsis chinensis. Pathogenicity was further tested using the ex-type strain (CFCC 52286) and another strain (CFCC 52288) on both detached branches and 3-year-old chestnut seedlings. The inoculation results showed that Gnomoniopsis chinensis is mildly pathogenic to Chinese chestnut. However, further studies are required to confirm its pathogenicity to the other cultivated Castanea species in America, Europe and Japan.