Sources of black Sigatoka resistance in wild banana diploids

Abstract Black Sigatoka (black leaf streak disease) is caused by the fungus Mycosphaerella fijiensisMorelet. This phytopathogen colonizes banana leaves, resulting in reduced photosynthesis and decreased productivity. Fungicide applications are useful to control black Sigatoka; however, they increase production costs and can have adverse environmental and health impacts. The cultivation of resistant cultivars is regarded as a more economically viable option. The objective of this study was to perform diploid phenotyping in a set of wild banana accessions to identify resistant genotypes. A total of 31 accessions (30 with AA genome and one with AB genome) were phenotyped based on the presence of disease symptoms using a scoring scale. The area under the disease progress curve (AUDPC), the disease severity index (DI), and the disease severity increase index (DII) were estimated. The DII variable proved to be efficient in identifying banana accessions with black Sigatoka resistance. Likewise, the selection index for ranking accessions with moderate black Sigatoka resistance allowed us to identify those genotypes with the highest quantitative resistance. Five diploid accessions (Krasan Saichon, Zebrina, Birmanie, Nº 118, and Tuu Gia) were found to be resistant to this fungal disease; eight accessions (PA Rayong, Pisang Cici, Malaccensis 1, 028003- 01, Microcarpa, Pisang Lidi, Lilin, and Malbut) were moderately resistant.摘要 黑条叶斑病（Black Sigatoka，又称黑叶条斑病）由斐济球腔菌（Mycosphaerella fijiensis Morelet）引起。该植物病原菌侵染香蕉叶片，导致光合作用减弱、产量下降。施用杀菌剂虽可防治黑条叶斑病，但会增加生产成本，且可能对环境与健康产生不利影响。培育抗病品种被视为更具经济可行性的方案。本研究旨在对一组野生香蕉种质开展二倍体表型鉴定，以筛选抗病基因型。本研究共纳入31份香蕉种质（30份为AA基因组，1份为AB基因组），基于病害症状表现采用分级评分标准开展表型分析，并估算了病情进展曲线下面积（AUDPC）、病情严重度指数（DI）及病情严重度增长指数（DII）。结果表明，DII变量可有效鉴定抗黑条叶斑病的香蕉种质。此外，用于排序中抗黑条叶斑病种质的选择指数，可帮助我们鉴定出数量抗性最强的基因型。本研究共鉴定出5份抗该真菌病害的二倍体种质：Krasan Saichon、Zebrina、Birmanie、Nº 118及Tuu Gia；8份为中抗种质：PA Rayong、Pisang Cici、Malaccensis 1、028003-01、Microcarpa、Pisang Lidi、Lilin及Malbut。