Abstract
In field peas, ascochyta blight is one of the most common fungal diseases caused by Didymella pinodes. Despite the high diversity of pea cultivars, only little resistance has been developed until to date, still leading to significant losses in grain yield. Rhizobia as plant growth promoting endosymbionts are the main partners for establishment of symbiosis with pea plants. The key role of Rhizobium as an effective nitrogen source for legumes seed quality and quantity improvement is in line with sustainable agriculture and food security programs. Besides these growth promoting effects, Rhizobium symbiosis has been shown to have a priming impact on the plants immune system that enhances resistance against environmental perturbations. This is the first integrative study that investigates the effect of Rhizobium leguminosarum bv. viceae (Rlv) on phenotypic seed quality, quantity and fungal disease in pot grown pea (Pisum sativum) cultivars with two different resistance levels against D. pinodes through metabolomics and proteomics analyses. In addition, the pathogen effects on seed quantity components and quality are assessed at morphological and molecular level. Rhizobium inoculation decreased disease severity by significant reduction of seed infection level. Rhizobium symbiont enhanced yield through increased seed fresh and dry weights based on better seed filling. Rhizobium inoculation also induced changes in seed proteome and metabolome involved in enhanced P. sativum resistance level against D. pinodes. Besides increased redox and cell wall adjustments light is shed on the role of late embryogenesis abundant proteins and metabolites such as the seed triterpenoid Soyasapogenol. The results of this study open new insights into the significance of symbiotic Rhizobium interactions for crop yield, health and seed quality enhancement and reveal new metabolite candidates involved in pathogen resistance.
Highlights
Legumes are the most important vegetable protein sources in food security programs (Kücük and Kivanc, 2008) as well as European animal feed production (Martin, 2014)
This study evaluates the effect of root nodulating Rhizobium as a plant growth promoting rhizobacteria (PGPR) microsymbiont on several quantity and quality components including seed metabolomics and proteomics analyses against ascochyta blight disease caused by D. pinodes in uninfected comparing to infected pea plants grown in pots for two cultivars with different levels of resistance
We focus on the following questions through integrated molecular and phenotypical approaches (a) does Rhizobium promote seed yield and quality in two pea cultivars of different susceptibility to D. pinodes infection; (b) how does pathogen infection influence seed quantity and quality; (c) does Rhizobium inoculation influence pathogen seed infection and how, and (d) are the effects of Rhizobium inoculation plant cultivar specific?
Summary
Legumes are the most important vegetable protein sources in food security programs (Kücük and Kivanc, 2008) as well as European animal feed production (Martin, 2014) They play a key role in the improvement of sustainable agriculture (Kumar et al, 2011). Ascochyta blight caused by Didymella pinodes is one of the most damaging diseases of pea (P. sativum) in major pea planting regions of the world (Setti et al, 2010; Ahmed et al, 2015). This disease reduces seed quality and causes severe yield losses (Garry et al, 1996). Due to the life cycle of disease as primary inoculum causing transmission of infection and in order to protect grain production, a few researches have studied the impact of biological control in disease management of seed infection caused by D. pinodes (Moussart et al, 1998)
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