In the present study, authors propagated Sophora tonkinensisGagnep plants using stem nodal culture. The results indicated that on MS medium supplemented with 30 g/l sucrose, 5.5 g/l agar, 200 ml/l coconut water, 1 g/l activated charcoal, 0.75 mg/l TDZ shoots proliferated from stem segments have the best count and height of shoots. The most appropriate medium for multiplication of shoots was the MS medium supplemented with 30 g/l sucrose, 5.5 g/l agar, 200 ml/l coconut water, 1 g/l activated charcoal, 0.75 mg/l TDZ, 0.5 mg/l IBA, 2.0 g/l peptone, 30 g/l carrot puree, pH 5.5 with the results of 20.60 shoots/explant, shoot height of 3.75 cm and 4.6 leaves/shoot after 8 weeks of culture. Root formation of shoots carried out on the MS medium supplemented with 30 g/l sucrose, 5.5 g/l agar, 200 ml/l coconut water, 1 g/l activated charcoal, 1.0 mg/l αNAA gave the best result. In the nursery, a mixture of humus + coconut fiber powder (70:30 ratio) was regarded as the best substrate due to the high survival rate of plantlets (92%) and healthy plantlets (10.30 cm high with 7.2 leaves and 4.3 new roots/a plantlet) at 10 weeks after planting

Pollen tube growth was examined to demonstrate the degree of self-incompatibility reaction in the pistils of 121 Citrus accessions including 77 pummelo accessions. One hundred of the 121 accessions were determined to be self-incompatible with the aid of an epifluorescent microscope. Based on the difference of self pollen tube growth between the self-incompatible and self-compatible accessions, the degree of selfincompatibility reaction in four portions of the pistils was roughly divided into three categories, i.e., high (H), moderate (M) and low (L). The degrees of the reaction in the stigmas, upper styles, middle styles and basal styles of these accessions were high-high-high-high (H-H-H-H), moderate-high-high-high (M-H-H-H), moderate-moderate-high-high (M-M-H-H), low-high-high-high (L-H-H-H), low-moderate-highhigh (L-M-H-H) or low-low-high-high (L-L-H-H) in order from the stigma to lower style, and were designated as H, MH, MMH, LH, LMH and LLH types respectively. All of 77 pummelo accessions examined were self-incompatible and all of the seven types of self-incompatibility reaction were observed in the accessions of which about 80% showed either H or MH type of reaction. The degree of self-incompatibility reaction was more variable in the pummelo accessions originating in Southeast Asia than those in Japan. In three mandarin relatives and four yuzu relatives, the H and MH types of self-incompatibility reaction were exclusively found. These results suggested that the degree of self-incompatibility reaction in each part of style was different in different Citrus accessions and showed geographical diversity. The reason for this is discussed.

Foot rot disease caused by Dickeya zeae in rice has been recently concerned in Vietnam, though there has not been a specific prevention and treatment measure. Streptomyces griseus strain VTCC 41724 has been previously reported for the antagonistic properties against Dickeya zeae and other plant pathogenic bacteria, it is therefore investigated for the capability of controlling this disease. Thus, the strain is selected for further studies aiming to application in organic rice cultivation. In this study, the appropriate culture conditions for strain VTCC 41724 to grow and release bioactive substances inhibiting D. zeae were determined, i.e. 2M medium, 5 days, 5% inoculum, and shaking at 160 rpm at 30C. A microbial formulation SGB was created from biomass of strain VTCC 41724 (7.1  108 CFU/g) and tested for its effectiveness in controlling the foot rot disease caused by Dickeya zeae under net house conditions. The experiment was carried out on Bac Thom No.7 rice variety, applied the SGB formulation in the soil before the seed and during the disease symptoms, has resulted in a protective efficiency as high as 73.56%. In addition, strain Streptomyces griseus VTCC 41724 also showed the antagonistic activity against harmful fungi including Phytophthora capsici, Alternaria sp., Colletotrichum gloeosporioides and Fusarium sp. This preliminary results showed the potential application of actinomycetes in biological control of foot rot caused by D. zeae, and other microbially mediated plant diseases.

Abstract. Nguyen XH, Nguyen TMN, Nguyen DH, Nguyen QC, Cao TT, Pham TTH, Nguyen TTT. 2023. Identification and characterization of Aspergillus niger causing collar rot of groundnut (Arachis hypogaea). Biodiversitas 24: 2556-2562. Groundnut (Arachis hypogaea L.) is an economically important legume crop in Vietnam and many other countries worldwide. Groundnut cultivation is affected by many biotic and abiotic stresses. Among biotic stresses, groundnut is attacked by many fungal, bacterial and viral pathogens. The most harmful fungal diseases are rust, stem rot, collar rot and other soil borne diseases. Collar rot caused by Aspergillus niger is one of the most important disease of groundnut extensive in Vietnam and worldwide. In this study, symptomatic infected plant samples were collected from nine different locations in Quang Tri and Thua Thien Hue provinces, Vietnam Isolated fungal species were identified on the basis of morphological characterization, and molecular level. The pathogenicity of fungal species was confirmed on the basis of Koch's postulates. The result showed that a total of nine fungal strains were isolated from infected groundnut samples. Morphological analysis results showed that all isolates exhibited A. niger characteristics, including black colony, biseriate conidia, hyaline conidiophores and sterigmata. Pathogenicity test showed that all nine A. niger isolates caused collar rot disease in groundnuts. Further molecular identification based on ITS1-4 region nucleotides comparison indicated that selected two isolates, namely QT1 and H17 belonged to A. niger. Further research should be done to find antagonistic microorganisms isolates for the bio-control of A. niger.