Resumo-O presente trabalho teve como objetivo estimar a divergência genética entre linhagens Pele de Sapo e entre linhagens Honey Dew. Foram avaliadas dez linhagens de melão Pele de Sapo e dez linhagens de melão Honey Dew, em experimentos separados, conduzidos em blocos casualizados com três repetições. A divergência genética foi estimada pela distância de Mahalanobis. Foram utilizados os métodos de Tocher e UPGMA para o agrupamento das linhagens. Para as linhagens Pele de Sapo, constatou-se divergência genética com a formação de quatro e cinco grupos conforme os métodos de agrupamento de Tocher e UPGMA, respectivamente. Sugere-se cruzamento das linhagens PS-01, PS-05 e PS-7 entre si ou com as demais linhagens do grupo I. Para as linhagens Honey Dew, verificou-se a formação dos mesmos três grupos nos métodos de agrupamento de Tocher e UPGMA. O grupo II formado pelas linhagens OF-01 e OF-02; o grupo III pela linhagem OF-03 e o primeiro grupo pelas demais linhagens. Com relação às linhagens Honey Dew, recomenda-se os cruzamentos das linhagens OF-01 ou OF-02, com as demais linhagens avaliadas. A linhagem OF-03, com características semelhantes às linhagens OF-01 ou OF-02 pode ser cruzada com as linhagens do grupo I. Palavras-chave-Cucumis melo. Heterose. Escolha de genitores. Distância de Mahalanobis.

The aim of this study was to evaluate the genotypic performance of twelve Piel de Sapo melon hybrids in the Mossoró-Assú agricultural region, state of Rio Grande do Norte, Brazil, using mixed models. Adaptability and stability of the predicted genotypic values were studied by the Harmonic Mean of the Relative Performance of Genotypic Values (HMRPGV) procedure. The traits evaluated were yield (Mg ha-1) and soluble solids content (ºBrix). The genotype x environment interaction was significant for the two variables in all the hybrid groups evaluated, with predominance of the complex part of the interaction, and this makes the selection process more difficult. Considering the genotypic values predicted, the HMRPGV method allowed identification of hybrids with greater genotypic adaptability and stability. The experimental hybrids HP-09 and HP-06 were more promising for growing in the Mossoró-Assú agricultural region since they have high stability and adaptability, as well as high yield and soluble solids.

Podosphaera xanthii is the most important causal agent of powdery mildew in melon, a crop ranked within the most economically important species worldwide. The best strategy to face this fungus disease, which causes important production losses, is the development of genetically resistant cultivars. Genetic breeding programmes require sources of resistance, and a few ones have been reported in melon, mostly in Momordica and Acidulus horticultural groups. However, the existence of many races that reduces the durability of the resistance makes necessary to find new resistant genotypes with different genetic backgrounds. In this work, Brazilian germplasm, together with a set of Indian landraces, and the COMAV's (Institute for the Conservation and Breeding of Agricultural Biodiversity) melon core collection, representing the whole variability of the species, were assessed for resistance against some common races in Spain and Brazil and genotyped with a 123-SNP (single nucleotide polymorphisms) genotyping platform to study the molecular relationships of the resistant accessions. In the first experiment, carried out in Valencia (Spain) in 2013, seventy-nine melon accessions were evaluated using artificial inoculation. Five accessions selected as resistant were also evaluated against races 1, 3, and 5 in Mossoró (Brazil, 2015) and against race 3.5 in Valencia (2016) under greenhouse conditions, and under four field conditions in Brazil. The accessions, AL-1, BA-3, CE-3, and RN-2, within the Brazilian collection, presented resistance against all the races of P. xanthii assayed in all conditions tested. AL-1, CE-3 and RN-2 were molecularly more similar to wild agrestis and Acidulus melons from Asia and Africa, while BA-3 grouped with Momordica types. Molecular analysis also confirmed that these new Brazilian sources of resistance differ from those previously reported, constituting interesting materials to encourage genetic breeding programmes, especially in Brazil and Spain.

-The aim of this study was to identify sources of resistance to

RESUMO Muitos fungos habitantes do solo acometem a lavoura meloeira, dentre estes, destaca-se o Myrothecium roridum que prejudica várias partes da planta, inclusive a semente. O presente trabalho estudou o efeito da inoculação de M. roridum sobre a germinação de sementes e crescimento de plântulas de acessos/cultivares de meloeiro, visando identificar genótipos com menor sensibilidade. O experimento foi realizado em delineamento inteiramente casualizados com quatro repetições em fatorial 38 x 2, em que o primeiro fator correspondeu aos acessos/cultivares, com 38 níveis, e o segundo, a inoculação, com dois níveis: com e sem inoculação. Foram avaliadas as características relativas à germinação (porcentagem e velocidade de emergência) e ao crescimento da plântula (altura, diâmetro do colo, peso seco da plântula e índice de área foliar). O fungo M. roridum afetou de forma negativa, a germinação, a velocidade de emergência e o desenvolvimento de plântulas dos acessos de meloeiro. Os acessos com menor sensibilidade ao fungo M. roridum foram A-6, A-8, A-19, A-22, A-39 e A-45.

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