Resistance to Xylella fastidiosa was evaluated in 264 hybrids of crosses between Murcott tangor (Citrus reticulata × Citrus sinensis) and Pera sweet orange (C. sinensis) under field conditions. Uninfected hybrids were grafted with buds collected from Pera sweet orange plants infected with X. fastidiosa, forming a plant with two scions (i.e., hybrid branches and Pera sweet orange branches). From these plants, we chose 10 genotypes with three biological replicates. We evaluated gene expression, bacterial multiplication, and citrus variegated chlorosis (CVC) symptom development in both scions. X. fastidiosa was not detected in most hybrid scions and none showed disease symptoms. In contrast, all Pera sweet orange scions were infected with X. fastidiosa and expressed symptoms of CVC. We quantified the expression of 12 defense-related genes by qPCR comparing resistant to susceptible scions. We suggest that some of these genes are involved in resistance of the hybrids to X. fastidiosa, since their expression was significantly higher in the resistant hybrid scions than in tolerant hybrids and scions originated from CVC symptomatic Pera sweet orange buds. However, we note that these data should be interpreted carefully, as the plant genotypes tested are related but necessarily distinct (hybrids of C. reticulata and C. sinensis, in relation to a C. sinensis control). A principal component analysis revealed a relationship between the expression of these genes and hybrid scions, and between scions that originated from infected buds and the presence of the bacteria and plant symptoms. Multiyear field trials are necessary to develop plant resistance to X. fastidiosa. While the experimental design used here had limitations, it allowed us to identify a set of genes potentially involved in Citrus sp. resistance to this pathogen. Future work on the role of these genes in plant defenses to X. fastidiosa infection is necessary to confirm their importance in the displayed resistance phenotype.
Arundina graminifolia é uma orquídea apreciada mundialmente pelo seu valor ornamental, possuindo também uso medicinal. Entretanto, os baixos investimentos relacionados a melhorias das atuais técnicas de cultivo in vitro, ferramenta importante para propagação de diversas espécies de orquídeas, impedem a diminuição dos custos de propagação. O presente trabalho teve por objetivo avaliar os efeitos do meio de cultura ½MS e de dois meios a base dos fertilizantes comerciais Hyponex® (NPK 6,5-6-19) e Kristalon laranja® (NPK 6-12-36), submetidos a três níveis de pH (5,3, 5,8 e 6,3), sobre o crescimento in vitro de A. graminifolia. Para tanto, sementes foram distribuídas em quatro frascos de cada meio e, após 180 dias de cultivo, foram retiradas aleatoriamente vinte plântulas de cada frasco para análise estatística. O meio de cultura mais eficiente foi o meio ½MS com nível de pH de 5,8, que apresentou as maiores médias para todas as variáveis analisadas.
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