Pre-Harvest Dark Spots Harm the Rice Grains Qualitatively and Quantitatively

Abstract

Rice grain dark spots are harmful, damaging the grains and, eventually, affecting the grain quality. Dark spots appear due to insect pests of the family Pentatomide, which feed on caryopsis tissues with a bite-puncture from the upper lip of their oral apparatus transformed into a needle. Mechanical damage to the grain leads to the penetration of microbes into the grain tissues, resulting in its darkening. The practical study aimed to determine the effects of the ripening stage on the ratio of dark spots on rice grains and their damage. Experiments assessed the influence of panicle age on rice grain damage caused by the southern green stink bug (Nezara viridula L.). Data recording on various parameters progressed by placing one and three bugs on the rice panicle. After crop maturity, evaluating the cut panicles continued based on empty grain content, grain size, and damaged grains. Other treatments had bugs placed during the flowering and five, 10, 15, 25, and 30 days after. Higher rice grain damage occurs when infested with three stick bugs in the first 10-15 days after flowering, revealing this period was the most vulnerable. Infection at later stages of ripening caused no significant damage to rice grains. The scientific literature does not provide information on dividing rice varieties into groups according to the degree of grain damage in the field in the form of dark spots. Based on the results, groups of pecky rice appeared for the first time according to the degree of damage, depending on the infection period, i.e., surface type, medium degree, and extensive damage type to the rice grains.