Kernel smut, caused by Tilletia horrida, is the disease characterized by the replacement of rice grains with black sooty masses of teliospores or chlamydospores. Kernel smut differs from rice false smut, caused by Ustilaginoidea virens, in the color of chlamydospores. False smut is characterized by globose, velvety spore balls ranging from orangish-yellow to greenish black in color. Both kernel smut and false smut have been persistent but are considered minor diseases in many countries since they were discovered in the late 1870s-80s, due to their sporadic outbreaks and limited economic impacts. In recent years, however, kernel smut and false smut have emerged as two of the most economically important diseases in rice, including organic rice, in many countries, especially in the US. The increased use of susceptible rice cultivars, especially hybrids, excessive use of nitrogen fertilizer, and short crop rotations have resulted in an increase in kernel smut and false smut, causing significant losses in grain yield and quality. In this article, we provide a review of the distribution and economic importance of kernel smut, our current understanding of the taxonomy, biology, and epidemiology of kernel smut, and the genomics of the kernel smut fungus as compared to false smut and its causal agent. We also provide an update on the current management strategies of pathogen exclusion, cultivar resistance, fungicides, biological control, and cultural practices for kernel smut and false smut of rice.
This study was conducted to determine whether currently prevailing isolates of Xanthomonas perforans and X. gardneri, the causal agents of tomato bacterial spot in Illinois, were resistant to copper. First, 133 isolates from each pathogen were tested for their multiplication on mannitol glutamate yeast agar (MGYA) amended with 0.8 mM of laboratory-grade copper sulfate. Results showed that 59% of X. perforans and 38% of X. gardneri isolates formed colonies on the copper-amended culture. Then, six isolates of X. perforans and five isolates of X. gardneri were tested for their multiplication on MGYA amended with 0.2, 0.8, 1.2, 1.6, and 2.0 mM of laboratory-grade of either copper hydroxide or copper sulfate. All 11 isolates formed colonies on cultures with 1.2 mM or lower rates of either copper compound. Molecular analysis revealed the presence of the copper-resistance genes copA and copM in the isolates. In vitro assays showed that both X. perforans and X. gardneri formed colonies when grown on Luria–Bertani agar containing low concentrations of copper hydroxide (Kocide-3000 46.1DF) and copper sulfate pentahydrate (Instill). Double Nickel LC, a biopesticide containing Bacillus amyloliquefaciens strain D747, was the most effective in preventing multiplication of copper-resistant isolates of both pathogens on the culture media.
An investigation was carried out to study the performance of mandarin grafts during 2017-18 at Banepa, Kavre to standardize suitable grafting time for two mandarin varieties. The experiment was conducted in two factorial Completely Randomized Design (CRD) with 10 treatments and three replications. The treatments consisted of combinations of five grafting dates (25 th November, 10 th December, 25 th December, 10 th January, and 25 th January) and two mandarin varieties (Dhankuta Local and Ota Ponkan). Scion collected from mother plants of respective mandarin varieties were grafted onto a trifoliate orange rootstock by side veneer method in the screen house. The results showed that grafting dates significantly affect the graft success and subsequent growth of grafted sapling of mandarin varieties. The highest graft success (100%) was observed on the grafts prepared in January. The sapling height (47.58 ± 1.93 cm), leaf area (32.74 ± 2.98 cm 2 ), number of primary branches per sapling (3.16 ± 0.20) and increased in diameter above union (17.78 ± 1.47%) were recorded maximum on the grafts prepared on 25 th January while the number of leaves per sapling (26.81 ± 1.84) was found superior for 10 th January grafted sapling. Most of the important parameters viz., graft success percent, sapling height, and leaf area were found nonsignificant for varieties but the number of leaves per sapling (23.99 ± 1.51), number of primary branches per sapling (2.72 ± 0.21), increased in diameter above union (16.24 ± 0.88%) and at union (13.72 ± 1.54%) was found maximum for Ota Ponkan. Therefore, the study revealed that late January was the most suitable time of grafting for both varieties of mandarin under Kavre, Nepal conditions.
Tilletia horrida, the causal agent of kernel smut of rice, is one of the most economically important diseases in rice. In recent years, increases in the incidence and severity of kernel smut have been reported across the rice growing-regions of the US. In this study, we report the draft genome sequences of seven strains of T. horrida. Among the seven strains, four were assembled to 26 mb in length and the remaining three to 20 mb in length. These genome sequence datasets will be valuable resources for future studies on the population genomics and fungicide resistance of T. horrida and the host-pathogen interactions.
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