The panicle branch, which is the key node for transport of photosynthesis products from source to sink, is vulnerable to many diseases caused by fungal pathogens, such as Magnaporthe oryzae, Cochliobolus miyabeanus. Among these diseases, rice blast is the most important one which causes devastating losses in many regions. In 2019 and 2020, panicle branch rot of rice with a symptom which could be mistaken with rice blast was observed in a paddy field, where is not traditional epidemical region of rice blast, in Fuyang, Zhejiang province. In 2020, similar symptom was also observed in Hubei and Anhui Province. In a paddy field in Fuyang, the symptom appeared on more than 30% investigated panicles. Diseased panicle exhibited brown to black lesions on primary or secondary branches as well as pedicels, however the grain and the neck of spike could not be infected which is the most obvious difference with rice blast. Obviously, the disease can't destroy the entire function of branch and blank grain was rarely observed, so its damage is not comparable with neck blast. Normally, it caused incomplete grain filing commonly leading to 5% - 25% grain weight loss. During the booting stage of rice, local solar irradiation time and temperature were fewer and lower than common years which may be responsible for losses caused by this disease. After surface sterilized, lesion parts cut from infected branches from 25 panicle samples were cultured on 2% water agar at 28℃ for 24-28 h, and fungi were isolated and purified by mycelial tip transferring. Among 31 isolates, 26 showed similar cultural characters. The wool-like mycelia were luxuriant and grew rapidly on PDA spreading the whole 9 cm petri dish in less than a week at 28 ℃. The mycelia were white to ashen at beginning and gradually turned black from center of the plate after 5 days culture at 28 ℃. Hyphae were smooth, branched, septate, hyaline or pale brown. Conidia were single-celled, black, spherical to subspherical, and 10.2 to 14.6 × 12.2 to 15.7 μm (n=50) in dimension and born on tip of hyaline and ampulliform conidiophores. The fungus showed similar morphological characteristics with Nigrospora oryzae (1). ITS sequences of 6 representative strains of the fungus were amplified, sequenced with primer pair, ITS1/ITS4 (2), and submitted into GenBank with an accession number, MW228165. Phylogenetic analysis was conducted with sequences of reference strains (3). The result showed that the fungus obtained in this study was fallen into the same group with N.oryzae. In view of above both morphological and molecular analysis, the strains were finally identified as N. oryzae. Pathogenicity tests were conducted in triplicate with rice panicles in initial heading stage. Fifty panicles were wounded on branches with needles and inoculated by spreading the conidia suspension (10μl, 1 × 106 conidia ml-1) on the wounds. The panicles used as control were treated in same way with 10μl of sterile water. The inoculated and control plants were kept in dark, 25 ℃ and relative humidity of more than 85% for 24 h in culture chamber. Symptoms appeared on 44 of 50 inoculated panicles which were basically similar with those observed in paddy field, while negative controls remained symptomless. The fungi re-isolated from inoculated panicles were also confirmed as N. oryzae by both morphological and molecular analysis. To the best of our knowledge, this is the first report of N. oryzae causing panicle branch rot disease on Oryza sativa (rice). This disease not only cause yield losses and lower milling quality, but could also be mistaken as rice blast incurring unnecessary fungicides spray.

Rice (Oryza sativa L.) is the most important and widely grown crop, covering about 29.9 million ha of total cultivation area in China. In the last decade, spikelet rot disease on rice became much more frequent in the middle and lower reaches of the Yangtze River, China. Fusarium proliferatum (Matsush.) Nirenberg ex Gerlach & Nirenberg was reported to be a causal agent of spikelet rot on rice in Hangzhou, Zhejiang province (Huang et al. 2012). In September 2019, a survey was conducted to understand the etiology of the disease in the main rice growing regions of Jinshan District of Shanghai. Symptomatic panicles exhibiting reddish or brown discoloration on the glumes were collected from different rice fields, where disease incidence was estimated to be between 20 to 80%. Diseased glumes were cut into small sections (5 × 5 mm) from the boundary of necrotic and healthy tissues, surface-sterilized with 75% ethanol for 30 s and 3% sodium hypochlorite for 90 s, rinsed twice with sterile distilled water, then placed onto 1/5 strength potato dextrose agar (PDA). After 3 to 5 days of incubation at 28°C in the dark, fungal growth with Fusarium-like colonies were transferred to PDA and purified by the single-spore isolation method. A total of 12 isolates were obtained and colonies showed loosely floccose, white mycelium and pale-yellow pigmentation on PDA. Microconidia were ovoid mostly with 0 to 1 septum, and measured 4.2 to 16.6 × 2.5 to 4.1 μm (n = 50). After 5-7 days of inoculation on carnation leaf agar (CLA), macroconidia produced usually had 3 to 5 septa, slightly curved at the apex, ranging from 15.7 to 39.1 × 3.3 to 5.0 μm (n = 50). Chlamydospores were produced in hyphae, most often solitary in short chains or in clumps, ellipsoidal or subglobose with thick and roughened walls. Molecular identification was performed on the representative isolates (JS3, JS9, and JS21). The rDNA internal transcribed spacer (ITS), translation elongation factor (TEF-1α) and β-tubulin (β-TUB) genes were amplified and sequenced using the paired primers ITS1/ITS4 (White et al. 1990), EF1/EF2 (O'Donnell et al. 1998) and T1/T22 (O'Donnell and Cigelnik 1997), respectively. The obtained sequences were deposited in GenBank under accession numbers MT889972 to MT889974 (ITS), MT895844 to MT895846 (TEF-1α), and MT895841 to MT895843 (β-TUB), respectively. BLASTn search of the sequences revealed 99 to 100% identity with ITS (MF356578), TEF-1α (HM770725) and β-TUB (GQ915444) of Fusarium incarnatum isolates. FUSARIUM-ID (Geiser et al. 2004) analysis showed 99 to 100% similarity with sequences of the F. incarnatum-equiseti species complex (FIESC) (FD_01651 and FD_01628). In addition, a phylogenetic analysis based on the concatenated nucleotide sequences placed the isolates in the F. incarnatum clade at 100% bootstrap support. Thus, both morphological observations and molecular criteria supported identification of the isolates as F. incarnatum (Desm.) Sacc (synonym: Fusarium semitectum) (Leslie and Summerell 2006, Nirenberg 1990). Pathogenicity tests were performed on susceptible rice cultivar 'Xiushui134'. At pollen cell maturity stage, a 2-ml conidial suspension (5 × 105 macroconidia/ml) of each isolate was injected into 10 rice panicles. Control plants were inoculated with sterile distilled water. Then, the pots were kept in a growth chamber at 28°C, 80% relative humidity, and 12 h/12 h light (10,000 lux)/dark. The experiment was repeated two times for each isolate. Two weeks post-inoculation, all inoculated panicles showed similar symptoms with the original samples, whereas no symptoms were observed on the control. The pathogen was re-isolated from inoculated panicles and identified by the method described above to fulfill Koch's postulates. Previous studies reported that F. incarnatum reproduced perithecia to overwinter on rice stubble as the inoculum of Fusarium head blight of wheat in southern China (Yang et al. 2018). To our knowledge, this is the first report of spikelet rot on rice caused by F. incarnatum in China. Further investigation is needed to gain a better understanding its potential geographic distribution of this new pathogen on rice crop. References: (1) Huang, S. W., et al. 2011. Crop Prot. 30: 10. (2) White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. (3) O'Donnell, K., et al. 1998. Proc. Natl. Acad. Sci. U.S.A. 95: 2044. (4) O'Donnell, K., Cigelnik, E. 1997. Mol. Phylogenet. Evol. 7: 103. (5) Geiser, D. M., et al. 2004. Eur. J. Plant Pathol. 110: 473. (6) Leslie, J. F., and Summerell, B. A. 2006. The Fusarium Laboratory Manual. Blackwell, Ames, IA. (7) Nirenberg, H. I. 1990. Stud. Mycol. 32: 91. (8) Yang, M. X., et al. 2018. Toxins. 10: 115. The author(s) declare no conflict of interest. Funding: Funding was provided by National Natural Science Foundation of China (grant no. 31800133), Zhejiang Provincial Natural Science Foundation of China (grant no. LQ18C140005), Key Research and Development Program of Zhejiang Province (grant no. 2019C02018), Shanghai Science and Technology for Agriculture Promotion Project (2019-02-08-00-08-F01127), and the Agricultural Science and Technology Innovation Program of China Academy of Agricultural Science (CAAS-ASTIP-2013- CNRRI).