Abstract
ABSTRACT White mold, caused by Sclerotinia sclerotiorum, is one the most devastating disease on soybean worldwide. Considering the potential of phosphites to protect plants against different diseases, this study investigated the possibility of using potassium (K), calcium (Ca), and zinc (Zn) phosphites for white mold control in soybean. The contact effect of the phosphites on fungal mycelial growth was evaluated in vitro. In the greenhouse study, plants were inoculated with S. sclerotiorum at 48 h after being sprayed with water (control), K, Ca, and Zn phosphites by using an agar plug (0.8 cm2) containing fungal mycelia. Lesion area of white mold and chlorophyll (Chl) a fluorescence parameters were evaluated on the leaflets of plants at 96 h after inoculation. The Chl a parameters were also evaluated in noninoculated leaflets at the same time. Fungal mycelial growth was abundant in the absence of phosphites, but inhibited in the presence of the three phosphites indicating their direct effect. The lesion area in the leaflets of plants sprayed with K, Ca, and Zn phosphites were 90, 98, and 68% lower, respectively, compared to plants sprayed with water. The functionality of the photosynthetic apparatus was more preserved on the leaflets of plants sprayed with phosphites due to the lower lesions size, especially for the Ca phosphite. In conclusion, the K, Ca, and Zn phosphites were effective in reducing white mold symptoms mainly through a contact effect on the fungal mycelial growth.
Highlights
White mold, caused by Sclerotinia sclerotiorum, is one the most devastating disease on soybean worldwide
Fungal mycelial growth and sporulation of pathogens can be both directly affected by phosphites or the host defense responses activity can be activated by them (Panicker and Gangadharan 1999; Daniel and Guest 2005; Dalio et al 2014; Novaes et al 2019; Fagundes-Nacarath et al 2018)
Considering the lack of information in the literature regarding the physiological changes in soybean plants sprayed with phosphites and infected with S. sclerotiorum, the present study aimed to examine the effect of potassium (K), calcium (Ca), and zinc (Zn) phosphites on the photosynthetic performance of the plants challenged or not with S. sclerotiorum by examining chlorophyll (Chl) a fluorescence parameters
Summary
Images of Chl a fluorescence on the leaflets obtained from noninoculated plants did not show any difference among the treatments regarding color patterns for the parameters Fv/Fm, Y(II), Y(NPQ), and Y(NO) (Fig. 4). Y(NPQ) was significantly higher by 26 and 18% for Ca and Zn phosphites treatments in comparison to the control treatment considering the inoculated leaflets (Fig. 5B). Y(II) was significantly higher by 119 and 215% for K and Ca phosphites treatments, respectively, in comparison to the control treatment (Fig. 5C). Regarding the Y(NO), there were significant reductions of 46, 26, and 16% for Ca, K, and Zn phosphites treatments, respectively, in comparison to the control treatment considering the inoculated leaflets (Fig. 5D). Lesions of white mold (a) and lesion area (LA) (b) in the leaflets of soybean plants sprayed with water (control) or with potassium (K), calcium (Ca), and zinc (Zn) phosphites at 96 h after inoculation with Sclerotinia sclerotiorum
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