The probenazole fungicide is used for controlling rice blast (Magnaporthe grisea) primarily by inducing disease resistance of the plant. To investigate the mechanism of induced plant defense, rice seedlings were treated with probenazole at 15 days post emergence, and non-treated plants were used for the control. The plants were infected with M. grisea 5 days after chemical treatment and incubated in a greenhouse. After 7 days, rice seedlings were sampled. The metabolome of rice seedlings was chemically extracted and analyzed using gas chromatography and mass spectrum (GC-MS). The GC-MS data were processed using analysis of variance (ANOVA), principal component analysis (PCA) and metabolic pathway elucidation. Results showed that probenazole application significantly affected the metabolic profile of rice seedlings, and the effect was proportionally leveraged with the increase of probenazole concentration. Probenazole resulted in a change of 54 metabolites. Salicylic acid, γ-aminobutyrate, shikimate and several other primary metabolites related to plant resistance were significantly up-regulated and some metabolites such as phenylalanine, valine and proline were down-regulated in probenazole-treated seedlings. These results revealed a metabolic pathway of rice seedlings induced by probenazole treatment regarding the resistance to M. grisea infection.

Unmanned aerial vehicles (UAVs) have been increasingly employed for fungicide applications in plant disease control. However, due to weight limitations, the fungicides sprayed through UAVs must be in low volumes with high concentrations in many instances, which may result in potential phytotoxicity. Here we evaluate the safety of low-volume spray of chemicals on rice plants. The plants were sprayed with propiconazole emulsifiable concentrate (EC) at 250 g/L mixed with various adjuvants and applied at a low volume, which contained the fungicide at concentrations equivalent to or higher than that used in UAV application. The spray adjuvants included YS-20, Biaopu adjuvant, TriTek, Yipinsongzhi, AgriSolv-C100, and Hongyuyan. Potential phytotoxicity on rice plants was examined based on surface tension and crop growth. Additives suitable for a low-volume spray of propiconazole were also assessed on three rice varieties for phytotoxicity. The results showed that after 72 h of fungicide application at 2, 4, and 8 times the recommended dose of 7500 μg/mL for UAV spray, rice leaves exhibited abnormal growth, and the dry weight of rice significantly decreased 21 days after application. Phytotoxicity was evaluated on three rice varieties 5 days after spraying propiconazole EC at 2 × recommended dose with one of the spray adjuvants. The addition of 1% YS-20, Biaopu adjuvant, TriTek, and Yipinsongzhi significantly augmented the phytotoxicity. However, both AgriSolv-C100 and Hongyuyan significantly reduced the comprehensive index of phytotoxicity and, therefore, could be used for UAV applications.

Objectives: To provide insights for breeding high-quality rice varieties, we analyzed local rice (Oryza sativa L.) germplasm from Yunnan Province, China, focusing on the relationships among Waxy gene alleles, indica–japonica differentiation, and amylose content (AC). Methods: We examined 201 local rice accessions. Two functional molecular markers for the Waxy gene were used to detect four alleles (Wx^a, Wx^b, Wxⁱⁿ, Wx^mw). Additionally, 33 InDel markers were employed to classify indica–japonica attributes, and AC was measured according to GB/T 15683-2008. Results: We detected 175 accessions with Wx^a, 20 with Wx^b, 4 with Wxⁱⁿ, and 2 with Wx^mw, indicating Wx^a dominance and a diverse genetic basis at the Waxy locus. Indica–japonica classification identified 180 indica-type, 19 japonica-type, and 2 intermediate-type accessions, confirming predominant indica differentiation in Yunnan rice. Integrating Waxy allele detection, indica–japonica attributes, and AC showed that Wx^a occurred primarily in indica rice with higher AC (mean 22.55%), comparable to Wxⁱⁿ (mean 24.33%); Wx^b was mainly found in japonica rice with lower AC (mean 13.46%), similar to Wx^mw (mean 15.65%). Conclusions: Local Yunnan rice exhibits Wx^a predominance at the Waxy locus and clear indica differentiation. The observed associations between Waxy alleles, subspecies attributes, and AC provide useful references for marker-assisted breeding of premium rice and for exploiting indica–japonica heterosis.

Biological control is an effective and environmentally friendly strategy for managing plant diseases. In this study, a broad-spectrum antagonistic bacterium, designated strain AN6, was isolated from rice plants and exhibited potent inhibitory activity against a variety of phytopathogens. In Oxford cup assays, AN6 suppressed the growth of Xanthomonas oryzae pv. oryzae (Xoo) by 73.60%, and its cell-free culture filtrate caused pronounced morphological deformation in the bacterial cells. Further in vitro assays, including dual-culture assays, volatile organic compound (VOC) assays, and cell-free supernatant (CFS) assays, demonstrated that AN6 also exerted strong antifungal effects against several pathogenic fungi. In addition, the strain was found to produce proteases and siderophores, which may contribute to its antagonistic capabilities. Taxonomic identification based on morphological traits, 16S rRNA and gyrA gene sequencing, average nucleotide identity (ANI), in silico DNA–DNA hybridization (isDDH), and phylogenetic analysis classified strain AN6 as Bacillus velezensis. Whole-genome sequencing revealed that AN6 harbors a 3,929,788 bp genome comprising 4025 protein-coding genes with a GC content of 46.50%. Thirteen biosynthetic gene clusters (BGCs) associated with the production of secondary metabolites—such as nonribosomal peptides, polyketides, and dipeptide antibiotics—were identified. The pot experiment further validated the biocontrol potential of AN6, achieving an 80.49% reduction in rice bacterial blight caused by Xanthomonas oryzae pv. oryzae. Collectively, these results indicate that B. velezensis AN6 is a promising candidate for development as a highly effective biocontrol agent for the integrated management of diverse plant diseases.