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Sorghum (Sorghum bicolor (L.) Moench) is an important food and fodder crop. Fungal diseases such as anthracnose caused by Colletotrichum sublineolum reduce sorghum yields. Genetic transformation can be used to confer tolerance to plant diseases such as anthracnose. The tolerance can be developed by introducing genes encoding proteins such as chitinases and chitosanases that hydrolyse fungal cell wall. Chitinases endolytically hydrolyse the b-1,4-linkages of chitin whereas, chitosanases hydrolyse the b-1,4-linkages between N-acetyl-D-glucosamine and D-glucosamine residues in a partially acetylated chitin polymer. Particle bombardment was used to genetically transform a sorghum genotype, KAT 412, with chitinase (harchit) and chitosanase (harcho) genes isolated from Trichoderma harzianum. Transgenic sorghum plants, KOSA-1-3, that expressed the two anti-fungal genes were developed. Expression of harchit and harcho in the transformants was confirmed by quantitative real time PCR. In planta and ex planta C. sublineolum infection assays were carried out using one-week old seedlings to determine tolerance to anthracnose. Seedlings from a transgenic line, KOSA-1, were found to be significantly more tolerant to anthracnose than the parent wild type, KAT 412. The transgenic line was further compared with other wild type sorghum cultivars. The comparison revealed a genotypedependent difference in anthracnose response. The transgenic line KOSA-1 was found to be more tolerant than the sorghum line SDSH 513 but less tolerant than KAT L5. This demonstrated the existence of genetic diversity, which together with the transgenes, could be utilised to pyramid genes for higher tolerance to anthracnose. The two antifungal genes introduced into sorghum genome could be introgressed into other sorghum lines for fungal diseases resistance.
Key words: Transgenic, sorghum, chitinase, chitosanase, Colletotrichum sublineolum, anthracnose