Precise Disease Severity Assessment for False Smut Disease of Rice

Abstract

False smut is a disease of rice inflorescence. The existing systems of disease severity assessment for rice false smut disease are not very sensitive as the ball quality and also the impact of false smut on filled grain number and grain‐filling were not under consideration. Here, a precise assessment method to evaluate the severity of the disease was developed. The ‘yield representative’ (YR) based on ‘mean floret wt.’ and ‘filled grain %’ was simulated for the precise disease severity assessment of rice false smut disease. The single floret weight envisages major yield components irrespective of the type of panicle. Correlation between YR and major yield attributes was studied, and it was observed that YR had significant correlation with ‘filled grain %’ (0.77–0.95) and ‘single spikelet weight’ (0.88–0.98). Significant negative correlation of YR was observed with the chaff percentage, false smut ball number and ball weight. This YR‐based methodology was utilized to assess the disease severity in nine rice cultivars. The disease severity in those nine cultivars was evaluated by the already existing methodologies also. The disease severity measured by the present technique was compared with the disease severity assessed by the old methodologies. The procedure adapted here for disease severity measurement was found to be more informative and useful. It was observed that in case of mild infection, the false smut was enhancing yield attributes. The high‐yielding rice varieties Savitri and Gayatri were found to be tolerant to false smut and may be used as resistant donors.

Current understanding on Villosiclava virens, a unique flower‐infecting fungus causing rice false smut disease

“…Similar results were presented in the data provided by Nessa et al (2015). Dhua et al (2015) also observed that small false smut balls (average ball weight of less than 40 mg) tended to be produced in tolerant rice cultivars. It will be interesting to address the underlying mechanism in the future.…”

“…We speculate that Vv may hijack the host nutrient reservoir by mimicking fertilization and activating the grain‐filling network, extracting nutrients towards colonization sites for growth and for the formation of false smut balls. Consistent with this hypothesis, a recent study has shown that mild Vv infection (one to two false smut balls per diseased panicle) can enhance rice yield attributes, such as the filled grain number and grain weight (Dhua et al ., ). Similar results were presented in the data provided by Nessa et al .…”

Rice False Smut: An Increasing Threat to Grain Yield and Quality

“…This finding is further supported by an independent study [63]. Although the underlying mechanism needs further investigation, the observation of V. virens activating rice grain filling could provide a promising explanation why mild V. virens infection enhances rice yield traits, including grain weight and filled grain number [9]. Identification and characterization of V. virens factors that manipulate rice grain filling should be an interesting research area in the future.…”

“…The disease induces considerable losses both in yield and quality [7,8], due to the occurrence of RFS balls and increased sterility of kernels adjacent to the balls [9]. Moreover, RFS balls produce two types of mycotoxins, i.e., ustiloxin and ustilaginoidin, which are poisonous to both humans and animals and impose significant health hazards by contaminating rice grains and straws [10][11][12].…”

The Flower-Infecting Fungus Ustilaginoidea virens Subverts Plant Immunity by Secreting a Chitin-Binding Protein

“…U. virens specifically infects rice flowers and develops into large mycelial colonies covered with massive chlamydospores, called false smut balls (Tang et al, 2013;Fan et al, 2016). Formation of false smut balls not only leads to considerable yield losses but also generates a diversity of mycotoxins poisonous to humans and animals (Zhou et al, 2012;Dhua et al, 2015). U. virensproduced mycotoxins mainly include ustiloxins and ustilaginoidins, which show cytotoxicities and phytotoxicities by inhibiting the mitosis process in eukaryotic cells (Zhou et al, 2012).…”