Rice is the staple food for over half of the world’s population. Infestation of Schizotetranychus oryzae (Acari: Tetranychidae) causes great losses in rice productivity. To search for rice genotypes that could better tolerate S. oryzae infestation, we evaluated morphological and production parameters in Brazilian cultivars, and identified two cultivars with contrasting responses. Leaf damage during infestation was similar for all cultivars. However, infestation in Puitá INTA-CL resulted in reduction in the number of seeds per plant, percentage of full seeds, weight of 1,000 seeds, and seed length, whereas infestation in IRGA 423 increased weight of 1,000 seeds and seed length. Reduction in seed weight per plant caused by infestation was clearly higher in Puitá INTA-CL (62%) compared to IRGA 423 (no reduction detected), thus Puitá INTA-CL was established as susceptible, and IRGA 423 as tolerant to S. oryzae infestation. Photosynthetic parameters were less affected by infestation in IRGA 423 than in Puitá INTA-CL, evidencing higher efficiency of energy absorption and use. S. oryzae infestation also caused accumulation of H2O2, decreased cell membrane integrity (indicative of cell death), and accelerated senescence in leaves of Puitá INTA-CL, while leaves of IRGA 423 presented higher levels of total phenolics compounds. We performed proteomics analysis of Puitá INTA-CL and IRGA 423 leaves after 7 days of infestation, and identified 60 differentially abundant proteins (28 more abundant in leaves of Puitá INTA-CL and 32 in IRGA 423). Proteins related to plant defense, such as jasmonate synthesis, and related to other mechanisms of tolerance such as oxidative stress, photosynthesis, and DNA structure maintenance, together with energy production and general metabolic processes, were more abundant in IRGA 423. We also detected higher levels of silicon (as amorphous silica cells) in leaves of infested IRGA 423 plants compared to Puitá INTA-CL, an element previously linked to plant defense, indicating that it could be involved in tolerance mechanisms. Taken together, our data show that IRGA 423 presents tolerance to S. oryzae infestation, and that multiple mechanisms might be employed by this cultivar. These findings could be used in biotechnological approaches aiming to increase rice tolerance to mite infestation.
6Infestation of Schizotetranychus oryzae (Acari: Tetranychidae) causes great losses in 3 7 rice productivity. Infestation in Puitá INTA-CL cultivar reduced the number of 3 8 seeds/plant, percentage of full seeds, 1,000 seeds weight, and seed length, whereas 3 9 infestation in IRGA423 increased 1,000 seeds weight and seed length. Reduction in 4 0 seed weight/plant caused by infestation was higher in Puitá INTA-CL than IRGA423. 4 1 Thus, Puitá INTA-CL was established as susceptible, and IRGA423 as tolerant to S. 4 2 oryzae infestation. Photosynthetic parameters were less affected by infestation in 4 3 IRGA423 than in Puitá INTA-CL. Infestation also caused accumulation of H 2 O 2 , 4 4 decreased cell membrane integrity and accelerated senescence in leaves of Puitá INTA-4 5 CL, while leaves of IRGA423 presented higher levels of phenolics compounds. Using 4 6 proteomic analysis, we identified proteins related to plant defense, such as jasmonate 4 7 synthesis, and related to other mechanisms of tolerance such as oxidative stress, 4 8 photosynthesis, and DNA structure maintenance, more abundant in IRGA423 after 4 9 7 1damage caused by arthropod pests can exceed 15% annually (Mitchell et al., 2016). In 7 2 order to quantify the pest resistance of the cultivars, the best tool does not seem to be 7 3 the increase of the arthropod population, but the measurement of the damages caused to 7 4 the plants, since the reduction of the leaf damage is followed by an increase in yield and 7 5 quality of the grain, and these are the ultimate objectives of most crop breeding 7 6 programs (Smith, 2005). Thus, the plant resistance/tolerance to arthropods is the sum of 7 7 genetically inherited traits that result in an adapted species that suffers less damage 7 8 compared to susceptible ones. These resistance/tolerance qualities should be measured 7 9 on a relative scale by comparing levels of damage and productivity with susceptible 8 0
4Rice (Oryza sativa L.) ssp. indica is the most cultivated species in the South of Brazil.
It is largely known that low temperature stress can affect rice (Oryza sativa L.) development and yield. However, most studies have focussed on unique and uninterrupted cold treatment, which is not representative of cold conditions for early sowing in temperate and subtropical areas where cold nights are followed by warm days during early vegetative stages. In order to elucidate whether rice plants could recover from the damages caused by repetitive cold nights, we submitted a cold-tolerant (CT) and a cold-sensitive (CS) indica genotype to 28 cold nights (10°C) followed by warm days (26°C) and analysed the developmental and productivity traits of plants cultivated in greenhouse and field conditions. While CT plants were able to recover from cold damage without significant development and seed production penalties, CS plants were affected, presenting lower results in plant height, tiller number, number of seeds per plant, % of full seeds per plant, grain length and area, weight of 1000 full grains, and grain weight per plant, with a grain yield reduction of 82% and 30% when cultivated in greenhouse and field conditions, respectively. Such data on sowing period, night temperatures and the cold response of the rice cultivar used are important for the producer to consider.
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