This is the first comprehensive study to identify fungal pathogens of mango (Mangifera indica L.) inflorescences in Puerto Rico. A total of 452 mango inflorescences were collected from four cultivars at seven developmental stages during two blooming seasons. Samples were gathered from the germplasm collection at the Agricultural Experiment Station of the University of Puerto Rico in Juana Díaz, Puerto Rico. Eight different symptoms were observed: cankers, flower abortion, powdery mildew, rachis necrotic lesions, rachis soft rot, tip blight, vascular wilt, and insect perforations with necrotic borders. Necrosis was the most prevalent symptom (47%), followed by powdery mildew (19%) and tip blight (6%). Symptoms of malformation were never observed in the field. Using a modified Horsfall and Barratt scale, data on all mango cultivars pooled from two blooming seasons showed that the full bloom stage, the last inflorescence developmental stage (G), displayed the highest mean disease severity (42.67%). This severity value was significantly higher than those of the other developmental stages evaluated (P<0.05). Early inflorescence developmental stages were asymptomatic or showed the lowest percentage of disease severity. An ANOVA was performed to compare disease severity among all mango cultivars regardless of developmental stage. Results showed that there were significant differences (P<0.05) between mean disease severity of cultivars ‘Parvin’ and ‘Haden’. Mean disease severity was higher in ‘Haden’ (20%) when compared to ‘Parvin’ (10.7%). There were no statistical differences in mean disease severity between cultivars ‘Irwin’, ‘Keitt’ and ‘Parvin’, or between ‘Irwin’, ‘Haden’ and ‘Keitt’. In addition to the powdery mildew caused by Pseudoidium anacardii, 26 genera of fungi, mainly of Ascomycetes, were identified from a total of 569 fungal isolates, from symptomatic and asymptomatic inflorescences. The most common fungi were: Diaporthe spp. (29%), followed by members of the Botryosphaeriaceae (16%), Curvularia spp. (11%) and Fusarium spp. (11%). Many fungal pathogens identified in this study were isolated from asymptomatic tissue, occurring as endophytes or latent pathogens: A. alternata, various members of the Botryosphaeriaceae, C. gloeosporioides complex, Cladosporium spp. and F. decemcellulare. Thus, the use of protectant fungicides will not be as effective as systemics in their control. Correct identification of fungal pathogens affecting mango inflorescences is important when quarantine regulations are applied. In addition, this information will facilitate the development of better management strategies in mango orchards.
Characterization of Resistance Mechanisms to Powdery Mildew (Erysiphe betae) in Beet (Beta vulgaris)
