Molecular Screening of Rice Cultivated in Benin for the Identification of Xanthomonas oryzae Pv. oryzae and Bacterial Leaf Blight Resistance Genes

One of the most devastating diseases of rice worldwide is bacterial blight (BLB) caused by Xanthomonas oryzae pv. Oryzae (Xoo). In Benin, Xoo was first described in 2013 on wild rice Oryzae longistaminata. So far, no study has been done on Beninese Xoo strains. We do not know whether the pathogen has already passed into the rice varieties grown, or if they are exposed to other bacteria. Whereas the use of resistant varieties, carrying resistance genes, is the only highly effective and environmentally friendly way to control this disease, no information is available on these Xoo resistance genes in rice varieties grown in Benin apart from the one we recently. This study aims to identify Beninese Xoo strains, causing BLB and screen rice varieties grown in Benin for the main resistance genes. Diseased rice leaves showing typical symptoms of fire blight collected from different rice fields in the three phytogeographic areas of Benin were analyzed by PCR for Xoo-specific sequence identification. Furthermore, seventy-five collected rice accessions were screened to identify xa5, Xa7, xa13, and Xa21 resistance genes to Xoo. The results reveal that Xanthomonas oryzae was identified in two fields in Banikouara and one in Malanville. On the other hand, Sphingomonas sp. has been identified in several other rice fields in Benin. Forty-seven of seventy-five rice accessions examined (62.66%) carried Xoo resistance genes with 3 (4%) and 40 (53.33%) of xa5 and Xa21 respectively. None of the accessions had either Xa7 or xa13 resistance genes. Three accessions possess both xa5 and Xa21 genes. Isogenic lines IRBB60 and IRBB21, supposed to be a positive control, presented a Xoo sensitivity allele. These results indicate that Xoo has moved from the wild rice variety to the cultivated variety in northern Benin and varietal improvement programs must be implemented with varieties having several resistance genes for the efficient response against a possible BLB pandemic in Benin.

Sensory Phenotypic and Molecular Identification of Aromatic Rice Accessions Cultivated in Benin

Rice is one of the most widely cultivated cereals in the world, and its aroma is increasingly in demand. With the advancement of research, a major rice flavor gene has been identified on rice chromosome 8. It encodes non-functional betaine aldehyde dehydrogenase leading to the accumulation of 2-acetyl-1-pyrroline which is the major olfactory compound that confers the fragrant character to rice. The aroma of rice is considered a special trait of enormous economic importance that determines the prime price in world trade. To satisfy the needs of the population and reduce rice imports into Benin, we conducted this study to identify aromatic rice accessions grown in Benin. Seventy-two rice accessions collected across Benin were PCR amplified with three SSR markers RM 7049, Aro 7, and RM 223, linked to the fgr (fragrance of rice) aroma gene. Molecular analysis revealed that 12 of the 72 accessions, namely Bagou 19, Bagou 22, Tchaka 34, Foun 15, Tchaka 41, Nana 32, Kan 61, Kung 69, Kung 67, Bagou 20, Agbab 101 and Koum 55 possess the fgr gene and can be considered as aromatic rice accessions. A sensory phenotypic test using KOH was carried out on rice accessions carrying fgr gene. Of the twelve positives, only one had the smell of aromatic rice, like the Azucena control. These results show that Benin also has aromatic rice varieties that can be sold on national and international markets.