Reduced arbuscular mycorrhizal colonization in tomato ethylene mutants Reduzida formação de micorrízas arbusculares em tomateiros mutantes em etileno

Plant hormones are likely key regulators of arbuscular mycorrhizae (AM) development. However, their roles in AM are not well known. Here mutants in five hormone classes introgressed in a single tomato (Lycopersicon esculentum Mill. Syn Solanum lycopersicum L.) background (cv. Micro-Tom) were used to determine their effects on AM development and the expression of defense-related genes (chitinases and b-1,3-glucanases) in roots. Under low P conditions, mutant epinastic (epi) and Never ripe (Nr), ethylene overproducer and low sensitivity, respectively, had the intraradical colonization by Glomus clarum highly inhibited, as compared to the control Micro-Tom (MT). No significant alterations in fungal colonization were observed in mutants affecting other hormone classes. Under low P conditions, the steady state levels of transcripts encoding a class I basic chitinase (chi9) were higher in mycorrhizal epi and Nr mutant roots as compared to MT controls. In contrast the steady state levels of a class III acidic b-1,3-glucanase (TomPR-Q'a) transcripts in mycorrhizal epi mutant roots were significantly lower than in mycorrhizal MT roots. Root colonization in epi mutants was accompanied by several alterations in fungal morphology, as compared to root colonization in MT controls. The data suggest that ethylene may play an important role in controlling intraradical arbuscular mycorrhizal fungal growth.<br>Os hormônios vegetais são possíveis reguladores chave do desenvolvimento de micorrizas arbusculares (MAS). Contudo, seus papéis em MA são pouco conhecidos. No presente estudo, foram utilizados mutantes em cinco classes hormonais introgredidos em uma única cultivar (cv. Micro-Tom) de tomateiro (Lycopersicon esculentum Mill. Syn Solanum lycopersicum L.) para determinar seus efeitos no desenvolvimento de MA e expressão de genes relacionados à defesa (quitinases e b-1,3-glucanases) em raízes. Sob condição de baixo P, os mutantes epinastic (epi) e Never ripe (Nr), os quais são super produtores e pouco sensíveis a etileno, respectivamente, tiveram a colonização intra-radicular por Glomus clarum inibida quando comparada com o controle Micro-Tom (MT). Não se observou alterações significativas na colonização fúngica nos mutantes afetando outras classes hormonais. Sob condição de baixo P, o nível de transcritos codificando uma quitinase básica de classe I (chi9) foi mais elevado em raízes micorrizadas dos mutantes epi e Nr, quando comparado com o controle MT. Em contraste, o nível de transcritos de uma b-1,3-glucanase ácida da classe III (TomPR-Q'a) em raízes micorrizadas do mutante epi foi significativamente menor que em raízes micorrizadas de MT. A colonização de raízes no mutante epi foi acompanhada por várias alterações na morfologia fúngica, quando comparada com o controle MT. Os resultados sugerem que o etileno pode desempenhar um importante papel controlando o crescimento fúngico intra-radicular nas MAS

The need to breed crop varieties suitable for organic farming, using wheat, tomato and broccoli as examples: A review

It is estimated that more than 95% of organic production is based on crop varieties that were bred for the conventional high-input sector. Recent studies have shown that such varieties lack important traits required under organic and low-input production conditions. This is primarily due to selection in conventional breeding programmes being carried out in the background of high inorganic fertilizer and crop protection inputs. Also, some of the traits (e.g., semi-dwarf genes) that were introduced to address problems like lodging in cereals in high-input systems were shown to have negative side-effects (reduced resistance to diseases such as Septoria, lower protein content and poorer nutrient-use efficiency) on the performance of varieties under organic and low-input agronomic conditions. This review paper, using wheat, tomato and broccoli as examples, describes (1) the main traits required under low-input conditions, (2) current breeding programmes for organic, low-input agriculture, (3) currently available breeding and/or selection approaches, and (4) the benefits and potential negative side-effects of different breeding methodologies and their relative acceptability under organic farming principles. © 2010 Royal Netherlands Society for Agricultural Sciences. Published by Elsevier B.V. All rights reserved