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J.A. López-Valenzuela, O. Martínez and O. Paredes-López

Fifteen mango cultivars were examined using randomly amplified polymorphic DNA (RAPD) markers with decamer primers of arbitrary sequence. Thirteen of the 40 primers screened were informative and 109 amplified DNA bands were selected as RAPD markers. Specific RAPD markers for some mango cultivars were identified. Cluster analysis based on the 109 RAPD markers produced a dendrogram of the genetic relatedness of the 15 mango cultivars. `Manila' and `Carabao' were the most similar, which is in good agreement with their putative pedigrees. The four major bifurcations in the dendrogram separated correctly the genotypes into four groups according to their geographic origin. Bulk segregant analysis of polyembryonic and monoembryonic cultivars detected a specific RAPD marker for polyembryony. These markers may facilitate the management of mango germplasm for breeding purposes.

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M.E. Valverde, P. Fallah Moghaddam, M.S. Zavala-Gallardo, J.K. Pataky, O. Paredes-Lopez and W.L. Pedersen

Ear gall development was evaluated after inoculating sweet corn (Zea mays L.) hybrids with Ustilago maydis (DC) Corda by injecting sporidial suspensions into silk channels when silks had emerged ≈3 to 6 cm from ear shoots. Gall incidence was ≈35% in two inoculation trials. About 0.5% of the noninoculated control plants was infected. Gall weight increased ≈250% to 500% between 14 and 21 days after inoculation, reaching a maximum of ≈280 to 600 g. Gall tissue was nearly 100% black and had lost its spongy integrity 19 to 21 days after inoculation, when mycelial cells formed powdery teliospores. A 1- or 2-day harvest window during which huitlacoche yield and quality were optimized corresponded to the time at which 60% to 80% of the gall tissue was black. The optimal huitlacoche harvest time varied among hybrids from 17 to 19 days after inoculation, but we suspect that optimal harvest time varies from ≈15 to 24 days after inoculation, depending on the growth stage at which the host is inoculated and the environmental conditions following inoculation. Differences among sweet corn hybrids in gall incidence, gall size, and coverage of mature galls by husk leaves were observed and could be used to select sweet corn hybrids that are well suited for producing huitlacoche.