Relationships between Microsclerotia Content and Hyperspectral Reflectance Data in Soybean Tissue Infected by Macrophomina phaseolina

Alternative methods are needed to assess the severity of charcoal rot disease [Macrophomina phaseolina (Tassi) Goid] in soybean [Glycine max (L.)] plant tissue. The objective of this study was to define the relationship between light reflectance properties and microsclerotia content of soybean stem and root tissue. Understanding that relationship could lead to using spectral reflectance data as a tool to assess the severity of charcoal rot disease in soybean plants, thus reducing human bias associated with qualitative analysis of soybean plant tissue and cost and time issues connected with quantitative analysis. Hyperspectral reflectance measurements (400-2490 nm) were obtained with a non-imaging spectroradiometer of non-diseased and charcoal rot diseased ground stem and root tissue samples of six soybean genotypes (“Clark”, “LD00-3309”, “LG03- 4561-14”, “LG03-4561-19”, “Saline”, and “Y227-1”). Relationships between the reflectance measurements and tissue microsclerotia content were evaluated with Spearman correlation (rs) analysis (p < 0.05). Moderate (rs = ±0.40 to ±0.59), strong (rs = ±0.60 to ±0.79), and very strong (rs = ±0.80 to ±1.00) negative and positive statistically significant (p < 0.05) monotonic relationships were observed between tissue spectral reflectance values and tissue microsclerotia content. Near-infrared and shortwave-infrared wavelengths had the best relationships with microsclerotia content in the ground tissue samples, with consistent results obtained with near-infrared wavelengths in that decreases in near-infrared spectral reflectance values were associated with increases in microsclerotia content in the stem and root tissue of the soybean plants. The findings of this study provided evidence that relationships exist between tissue spectral reflectance and tissue microsclerotia content of soybean plants, supporting spectral reflectance data as a means for assessing variation of microsclerotia content in soybean plants. Future research should focus on the modelling capabilities of the selected wavelengths and on the feasibility of using these wavelengths in machine learning algorithms to differentiate non-diseased from charcoal rot diseased tissue.

大豆炭腐病菌生物学特性的研究

大豆炭腐病是大豆重要病害,高温、干旱的气候条件有利于病害的发生。本试验研究了引起大豆炭腐病病原菌菜豆壳球孢分离物的生物学特性。结果表明,该病原菌生长的温度范围为15～40℃,最适温度为35℃;pH范围为3～12,最适pH值为5;在含有120 mmol/L KClO3的PDA培养基上呈致密型生长类型。用蔗糖、PEG 6000和NaCl作为胁迫剂研究干旱胁迫对该病原菌生长影响,结果表明,一定浓度的蔗糖(100～500 mmol/L)、PEG 6000(10%～30%)和NaCl(100～300 mmol/L)均有利于病原菌菌丝生长;低水势环境对菌核的形态有一定的影响,且不利于菌核的产生。综合以上结果,大豆炭腐病病菌喜好高温、偏酸性和低湿环境。