Selection of plum genotypes for resistance to leaf scald

ABSTRACT Plum (Prunus salicina Lindl.) cultivation is seriously compromised in Brazil due to the occurrence of leaf scald, a disease caused by the bacterium Xylella fastidiosa subsp. multiplex. The objective of this study was to evaluate plum genotypes agronomically promising for resistance to leaf scald, under natural conditions of occurrence of the disease. Ten out of 50 plum genotypes belonging to the germplasm bank of “Instituto Agronômico do Paraná (IAPAR)” were selected. Five evaluations of leaf scald severity were carried out from January to February (2017 and 2018). Polymerase chain reaction (PCR) was also performed for samples of these genotypes to determine the presence of the bacterium X. fastidiosa subsp. multiplex. The genotypes differed in relation to their susceptibility to leaf scald. PR-1095 was the most resistant genotype and did not show any leaf symptom of the disease. In contrast, genotypes PR-1126 and PR-1137 had the greatest susceptibility to the disease, showing severe scald symptoms. However, PCR revealed the presence of the bacterium even in the most resistant genotypes, indicating, for example, that PR-1095, which had no symptoms of the disease, is probably tolerant to leaf scald.

Ketahanan Delapan Klon Abaka (Musa textilis) Terhadap Fusarium oxysporum F sp. cubesence

<p>Penyakit layu Fusarium pada tanaman Abaka (<em>Musa textilis </em>L.) yang disebabkan oleh <em>Fusarium oxysporum </em> f sp. c<em>ubesence </em>(<em>Foc</em>) merupakan salah satu kendala terhambatnya perkembangan Abaka di Indonesia karena menyebabkan penurunan kualitas serat. Gejala serangan Foc adalah terbelahnya batang semu bagian luar dan warna daun berubah menjadi kuning pucat sampai kuning kecoklatan kemudian layu. Indonesia belum memiliki varietas unggul untuk mendukung pengembangan Abaka, meskipun Balittas memiliki koleksi plasma nutfah yang cukup. Tulisan ini bertujuan untuk memberikan informasi ketahanan delapan klon Abaka yang memiliki potensi produksi tinggi terhadap infeksi <em>Foc</em>. Penelitian dilakukan di rumah kaca Balittas pada tahun 2018. Sebanyak delapan klon abaka (UB4, Tangongon, Tangongon 70-3-1-1-2, UB-7, Cilacap, UB-8, UB-11, dan UB-5) yang diuji disusun dalam Rancangan Acak Kelompok dengan tiga kali ulangan. Isolat <em>Foc</em> yang digunakan berasal dari tanaman abaka yang menunjukkan gejala layu Fusarium. Masing-masing klon ditanam dalam polibag berukuran 500 g satu tanaman per polibag. Setiap klon ditanam sebanyak 10 polibag per ulangan. Benih abaka berumur 3 bulan direndam selama 24 jam dalam suspensi konidia <em>Fo</em><em>c</em> dengan kerapatan10⁵/ml. Pengamatan kejadian penyakit dilakukan setiap 5 hari sekali sampai tanaman berumur 60 hari. Hasil penelitian menunjukkan bahwa, tidak ada klon abaka yang diujikan tahan terhadap <em>Foc</em><em> </em>melainkan rentan (UB8 dan Tangongon) dengan tingkat kejadian penyakit 43,3% - 46,7% dan sangat rentan (Cilacap, UB4, Tangongon 70-3-1-1-2, UB-7, UB-11, dan UB-5) dengan tingkat kejadian 56,7% - 96,7%<em>.</em></p><div><hr align="left" size="1" width="33%" /><div><p> </p></div></div><p align="center"><strong>Resistance of Eight Clones of Abaca (<em>Musa </em></strong><strong><em>t</em></strong><strong><em>extilis</em></strong><strong>) </strong><strong>t</strong><strong>o <em>Fusarium </em></strong><strong><em>o</em></strong><strong><em>xysporum</em></strong><strong> F </strong><strong>s</strong><strong>p. </strong><strong><em>c</em></strong><strong><em>ubesence</em></strong><strong></strong></p><p align="center"><strong>ABSTRACT</strong>.</p><p>Fusarium wilt on Abaca (<em>Musa textilis </em>L.) caused by <em>Fusarium oxysporum </em>f sp. c<em>ubesence </em>(<em>Foc</em>) was one of the obstacles to development of Abaca in Indonesia since it decreased fibre quality. Symptom of <em>Foc</em> infection was splitted of the outer low pseudostem and discoloured of the leaf sheat to pale yellow or brownish yellow and then wilt. Indonesia has not released a superior variety (ies) to support the development of Abaca, although Balittas has enough germplasm collection. This paper reported the resistance of eight Abaca clones, which have high potential production, to <em>Foc</em>. The trial activity has been conducted in the screen house of BALITTAS in 2018. The tested clones were: UB4, Tangongon, Tangongon 70-3-1-1-2, UB-7, Cilacap, UB-8, UB-11, and UB-5 which was arraned in randomized block design with three replicates. <em>Foc </em>was isolated diseased abaca with wilt and yellow leaf symptom. Each clone was grown in sterilised soil in a 500 g polybag, with 10 <em>three months old</em> plants for each replicate. The plants were soaked in conidial suspension (10⁵/ml) for 24 hours. Disease incidence was observed every five days for 60 days. Result of the test showed, none of the clones was resistant to <em>Foc</em><em> </em>but susceptible (UB8 and Tangongon) with disease incidence rates of 43.3% - 46.7% and very susceptible (Cilacap, UB4, Tangongon 70-3-1-1 -2, UB-7, UB-11, and UB-5) with an incidence rate of 56.7% - 96.7%, respectively.</p>

Coumestrol Confers Partial Resistance in Soybean Plants Against Cercospora Leaf Blight

Although previous research showed that the purple symptom of Cercospora leaf blight (CLB) is associated with lower biomass of Cercospora cf. flagellaris and lower concentrations of cercosporin, a reactive oxygen species producer, as compared with blighted leaves, the hypothesis that the purple symptom is a plant reaction to the pathogen has never been tested. In this study, we demonstrated that high levels of coumestrol (COU) were associated with purple symptoms of CLB and that COU has strong antioxidant activity. Additionally, we found that COU is restricted to the pigmented areas of purple leaves, and the pigmentation is restricted to the adaxial surfaces, suggesting that COU may be acting as a sunscreen. Even though COU is associated with the purple leaf symptom, this coumestan is not the direct cause of discoloration in that COU is colorless. Quantification of chlorophyll a and b and total carotenoids suggested that blighted but not purple or asymptomatic leaves were undergoing photooxidative stress. Because the purple symptom is associated with high COU concentrations, lower biomass of C. cf. flagellaris, and lower cercosporin concentrations, we conclude that the purple symptom is a disease resistance reaction, mediated in part by COU, which provides a high level of antioxidant activity and, hence, partial resistance.

RESISTANCE OF LOCAL BANANA VARIETIES TO FUSARIUM WILT DISEASE

Fusarium wilt is one of the important banana diseases that lead to low quality and quantity of banana production. The objective of this study was to examine and study the resistance of some local banana varieties to fusarium wilt. Pathogens were isolated from the weevil of kepok banana (saba banana) that showed severe symptoms of Fusarium wilt. The inoculum was prepared by propagating the pathogens on Potato Dextrose Agar (PDA) medium. Inoculation was carried out using mycelium fragment suspension (12 mg hyphae mL-1 tween 20 0.05%). The roots of the two-week Ambon banana were injured and immersed in the suspension. Pathogens were determined using Koch's postulates. The varieties tested were seven (7) local banana varieties grown in South Kalimantan. Levels of resistance were determined based on the scale of Leaf Symptom Index (LSI). The pathogens were identified as Fusarium oxysporum f.sp. cubense. The results showed that there were differences in the levels of resistance; Kepok banana (highly susceptible); yellow Ambon, Awa, Susu, Mahuli and Talas bananas (susceptible), and Manggala banana (tolerant).

Identification of Tobacco streak virus Associated With a Virus-like Mottle Symptom on Hosta

In this brief, the authors describe the identification of Tobacco streak virus associated with a virus-like leaf symptom on Hosta spp. The identity of the virus was confirmed by ELISA and PCR using cDNAs synthesized from dsRNA template and immuncaptured virions and primers to amplify the movement protein and capsid protein genes. This is the first report of TSV infecting Hosta in Ohio, and to our knowledge in the United States. Accepted for publication 17 December 2012. Published 22 January 2013.