In 2017 and 2018, a total of 294 Fusarium fujikuroi isolates were collected from bakanae-diseased rice plants in Jinhua, Shaoxing, and Jiaxing in Zhejiang Province, China. Phenamacril sensitivity of these isolates was determined by the 50% effective concentration value or minimum inhibitory concentration methods. Our results indicated that the phenamacril resistance frequency of F. fujikuroi increased from 18% in 2017 to 47% in 2018, and rice plants infected with F. fujikuroi-resistant isolates could not be protected effectively with 50 mg/liter of phenamacril. Phenamacril-resistant F. fujikuroi isolates obtained from rice fields showed stable resistance, because their fitness levels (i.e., mycelial growth, sporulation, and pathogenicity) were similar to the phenamacril-sensitive isolates. In addition to the point mutation at codon 219 in the myosin-5 gene that conferred resistance to phenamacril, our results also showed another point mutation at codon 218 (AAG→ACG) in myosin-5 that also conferred resistance to phenamacril. In this study, we found rapid development and persistence of diversified genotypes of phenamacril resistance, highlighting the importance of proper use of phenamacril in rice fields. Our results may also help researchers develop new fungicides or new control strategies using combinations of different fungicides in the control of phenamacril-resistant F. fujikuroi isolates.

In order to clarify the impacts of southern rice black-streaked dwarf virus (SRBSDV) infection on rice plants, rice planthoppers and natural enemies, differences in nutrients and volatile secondary metabolites between infected and healthy rice plants were examined. Furthermore, the impacts of virus-mediated changes in plants on the population growth of non-vector brown planthopper (BPH), Nilaparvata lugens, and the selectivity and parasitic capability of planthopper egg parasitoid Anagrus nilaparvatae were studied. The results showed that rice plants had no significant changes in amino acid and soluble sugar contents after SRBSDV infection, and SRBSDV-infected plants had no significant effect on population growth of non-vector BPH. A. nilaparvatae preferred BPH eggs both in infected and healthy rice plants, and tended to parasitize eggs on infected plants, but it had no significant preference for infected plants or healthy plants. GC-MS analysis showed that tridecylic aldehyde occurred only in rice plants infected with SRBSDV, whereas octanal, undecane, methyl salicylate and hexadecane occurred only in healthy rice plants. However, in tests of behavioral responses to these five volatile substances using a Y-tube olfactometer, A. nilaparvatae did not show obvious selectivity between single volatile substances at different concentrations and liquid paraffin in the control group. The parasitic capability of A. nilaparvatae did not differ between SRBSDV-infected plants and healthy plant seedlings. The results suggested that SRBSDV-infected plants have no significant impacts on the non-vector planthopper and its egg parasitoid, A. nilaparvatae.

No abstract

The susceptibility of rice lines, T1C-19, T2A-1, and MH63 to SRBSDV infection are similar and the contents of cry protein in T2A-1 and T1C-19 do not change significantly. The survival rates of BPH nymphs feeding on SRBSDV-infected T1C-19, Bt T2A-1, or MH63 rice plants were not significantly different. The developmental stages of female BPH fed on T1C-19 plants infected with SRBSDV were significantly shorter than those fed on uninfected rice, while the males showed no significant difference. The duration of BPH feeding on SRBSDV-infected T2A-1 and MH63 also showed no significant difference in comparison with the respective control groups. Longevities of BPH adults feeding on SRBSDV-infected T1C-19, T2A-1 or MH63 were also not significant. However, the longevity of male adult BPH feeding on un-infected MH63 was significantly reduced in comparison with that of adult males feeding on un-infected T1C-19 and T2A-1 rice. In addition, the different rice lines and the rice plants infected and uninfected with SRBSDV did not significantly affect the sex ratio, female body weight, longevity, fecundity, or egg hatchability of BPH. In general, transgenic Bt rice infected with SRBSDV had little effect on the ecological adaptability of BPH.

The genus Cucurbita comprises many popular vegetable and ornamental plants, including pumpkins, squashes, and gourds, that are highly valued in China as well as in many other countries. During a survey conducted in Zhejiang province, Southeast China in 2016, severe symptoms of viral infection were observed on Cucurbita maxima Duch. ex Lam. Diseased plants showed symptoms such as stunting, mosaicking, Shoe string, blistering, yellowing, leaf deformation, and fruit distortion. Approximately, 50% of Cucurbita crops produced in Jinhua were diseased, causing an estimated yield loss of 35%. In this study, we developed a method using all known virus genomes from the NCBI database as a reference to map small RNAs to develop a diagnostic tool that could be used to diagnose virus diseases of C. maxima. 25 leaf samples from different symptomatic plants and 25 leaf samples from non-symptomatic plants were collected from the experimental field of Jihua National Agricultural Technology Garden for pathogen identification. Small RNAs from each set of three symptomatic and non-symptomatic samples were extracted and sequenced by Illumina sequencing. Twenty-four different viruses were detected in total. However, the majority of the small RNAs were from Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV), and Cucumber mosaic virus (CMV). Mixed infections of these three viruses were diagnosed in leaf samples from diseased plants and confirmed by reverse transcription PCR (RT-PCR) using primers specific to these three viruses. Crude sap extract from symptomatic leaf samples was mechanically inoculated back into healthy C. maxima plants growing under greenhouse conditions. Inoculated plants developed the same disease symptoms as those observed in the diseased plants and a mixed infection of ZYMV, WMV, and CMV was detected again by RT-PCR, thus fulfilling Koch’s postulates. The diagnostic method developed in this study involves fewer bioinformatics processes than other diagnostic methods, does not require complex settings for bioinformatics parameters, provides a high level of sensitivity to rapidly diagnose plant samples with symptoms of virus diseases and can be performed cheaply. This method therefore has the potential to be widely applied as a diagnostic tool for viruses that have genome information in the NCBI database.