Abstract
Rice is a crop that is consumed as a staple food by the majority of the people in the world and therefore failure in rice crops, due to any reason, poses a severe threat of starvation. Rice blast, caused by a fungus Pyricularia oryzae, has been ranked among the most threatening plant diseases of rice and it is found wherever rice is grown. All of the rice blast disease management strategies employed so far have had limited success and rice blast has never been eliminated from rice fields. Hence, there is a need to look for the best remedy in terms of effectiveness, sustainability, and organic nature of the method. This study was aimed at determining the plant growth-promoting and fungicidal effects of a mixture of Piper caninum and Piper betle var. Nigra leaves extracts and rhizobacteria. Gas chromatography–mass spectrophotometry (GC-MS) analysis of a mixture of leaves extracts of these plants revealed the presence of new bioactive compounds such as alpha.-gurjunene, gamma.-terpinene, and ethyl 5-formyl 3-(2-ethoxycarbonyl) in a mixture of leaves extracts of P. caninum and P. betle var. Nigra. The mixture of these extracts reduced the intensity of blast disease, inhibited P. oryzae, and improved the growth, yield, and quality of Bali rice. All treatments comprising of different concentrations of a mixture of leaves extracts of P. caninum and P. betle var. Nigra plus rhizobacteria exhibited biocontrol and bioefficacy. However, a 2% concentration of a mixture of these leaves extracts with plant growth-promoting rhizobacteria (PGPR) exhibited potent inhibition of growth of P. oryzae, a significant reduction in the intensity of blast disease, and a maximum increase in growth, yield, and quality of Bali rice. In the 15th week, the intensity of blast disease decreased from 80.18% to 7.90%. The mixture of leaves extract + PGPR also improved the height of the plant, the number of tillers, number of leaves, number of grains per panicle, number of heads per panicle, and the full-grain weight per clump. Applications of various concentrations of a mixture of leaves extracts + PGPR resulted in improvement in the potential yield of rice, however, the application of 2% extracts + PGPR gave the highest potential yield of 5.61 tha−1 compared to the low yields in the control and other treatments. The high grain yield observed with the treatment was caused by the low intensity of blast disease. This treatment also strengthened the stem and prevented the drooping of the plant and improved the quality of rice grain.
Highlights
Rice is the principal food for the majority of the population in the world, and in Asia, it is consumed by 2.7 billion people
Rice blast caused by Pyricularia oryzae or Magnaporthe oryzae is among the major threats to rice productivity besides brown spot sheath blight, bacterial leaf blight, and sheath rot of rice
Rice blast epidemics in various parts of the world have resulted in about 50% to 90% and under extreme cases up to 100% losses in crop yield [3] compared to 20%–50% losses caused due to sheath blight, 50%–70% yield loss caused due to brown spot disease, 25% crop losses caused by bacterial leaf blight, and 20%–80% yield losses caused due to sheath rot disease [3]
Summary
Rice is the principal food for the majority of the population in the world, and in Asia, it is consumed by 2.7 billion people. Rice farming is one of the principal sources of income and employment for the majority of households across the world [3,4] It is an important cereal cultivated for food security and income by marginal farmers [5]. Rice blast epidemics in various parts of the world have resulted in about 50% to 90% and under extreme cases up to 100% losses in crop yield [3] compared to 20%–50% losses caused due to sheath blight, 50%–70% yield loss caused due to brown spot disease, 25% crop losses caused by bacterial leaf blight, and 20%–80% yield losses caused due to sheath rot disease [3]. The challenges to produce high quality, nutritive, and organic rice at lower costs continue all while in the presence of unforgiving and unrelenting pathogens [11]
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