Bacterial panicle blight (BPB) of rice ( Oryza sativa L.) occurs when the bacterium Burkholderia glumae Kurita and Tabei infects emerging and flowering panicles, causing kernels to abort. To identify quantitative trait loci (QTLs) for BPB resistance, a population of 300 recombinant inbred lines (RILs) derived from a cross between ‘Lemont’ and ‘TeQing’ were evaluated in 2001 and 2002 in field plots spray‐inoculated with B. glumae at the time of flowering. Because this RIL population had been previously used to map QTLs for three other diseases, present use of this population allowed direct comparison between the various disease resistance QTLs. Multiple interval mapping using QTL Cartographer v2.5 putatively identified 12 BPB QTLs, three of which were statistically significant in both years and found to have epistatic effects in 2002. TeQing was the source of resistance for eight QTLs; Lemont for four. Four BPB QTLs colocated with QTLs previously identified as providing resistance to one or multiple other diseases. Three BPB QTLs were also associated with late flowering. Because late flowering panicles are subjected to cooler temperatures that are less conducive to disease development during grain fill, it is possible that the genetic effects of the heading‐related QTLs were biased. The present data could not distinguish between pleiotropy and close linkage of the BPB QTLs with the previously identified heading and disease resistance QTLs.
Abstract ‘PVL02’ (Reg. no. CV‐158, PI 691607), a Provisia (BASF) long‐grain rice ( Oryza sativa L.) cultivar, was developed by the Louisiana State University Agricultural Center at the H. Rouse Caffey Rice Research Station near Crowley, LA, and approved for release in 2019. PVL02 is the second rice cultivar released as part of the Provisia Rice System with resistance to Provisia herbicide, containing the active ingredient quizalofop‐p‐ethyl, an AACase (Group 1) herbicide. PVL02 was derived from the cross ‘Cheniere’/BASF1‐5 and advanced as an F 2:3 row based on agronomic characteristics. Testing in the Provisia preliminary yield trial in 2014 and the Provisia multi‐location test in 2015 indicated good yield potential and favorable agronomic characteristics. In 2016, 2017, and 2018, PVL02 was evaluated in 26 replicated trials across seven locations in Louisiana. Four high‐yielding commercial cultivars were included as checks: ‘Jupiter’, ‘CL153’, ‘Cheniere’, and ‘PVL01’. The grain yield of PVL02 was 8.2 t ha −1 compared with 9.2 t ha −1 for Jupiter, 8.6 t ha −1 for CL153, 8.5 t ha −1 for Cheniere, and 7.6 t ha −1 for PVL01. PVL02 was taller than the checks. The milled grain length was shorter than typical long grains, with a length‐to‐width ratio of 2.81. It has a typical US long‐grain rice cooking quality with intermediate amylose and gel temperature. PVL02 is moderately susceptible to sheath blight, Cercospora spp., and leaf blast and susceptible to bacterial panicle blight.
Individual plants from the first through third backcrosses of the rice sheath blight-resistant cultivar Tetep to the susceptible cultivar Lemont were selected for low infection cushion counts and for resistant-type lesions in the greenhouse. Replicated progeny field tests of selfed plants from each generation were conducted. Correlations between individual backcross plants, rated for number of infection cushions and lesion type, and disease ratings of their field-tested progeny were relatively low but resistance levels were maintained (.)
White leaf streak, caused by Mycovellosiella oryzae (Deighton and Shaw) Deighton (syn. Ramularia oryzae), was found in Louisiana rice. The symptoms closely resemble those of narrow brown leaf spot caused by Cercospora janseana (Racib.) O. Const. (syn. C. oryzae (Miyake)), and it is difficult to distinguish between these two diseases. Initially both produce similar elongated light brown lesions, but later the lesions of white leaf streak become wider with a whitish center and are surrounded by a narrow light brown margin (2,3). The disease was first observed at the Rice Research Station, Crowley, LA, in 1996 on older leaves of the cultivar Lemont at maturity. Leaves containing the unusual lesion types were placed in a moist chamber and incubated at 28°C for 5 days. Abundant conidia were produced and the fungus was isolated on acidified potato dextrose agar (APDA) by single spore isolation and by plating infected tissues after surface sterilization in 40% Clorox for 10 to 15 min. The colonies grew slowly on APDA and were dark gray in color. The conidia formed in branched chains or singly. They were hyaline, cylindrical with tapering ends and a thick hilum; 0 to 3 septate, and 15 to 35 m long (1,3). Pathogenicity tests were conducted in the greenhouse on the Lemont and Cypress rice cultivars by spraying a conidial suspension (103-4 conidia per ml) onto leaf blades at boot stage. Conidia were produced by growing the fungus on PDA for 10 to 14 days. Inoculated plants were placed inside a humid chamber in a greenhouse and maintained for 4 to 5 weeks. Many elongated lesions similar to those observed in the field were produced 3 to 4 weeks after inoculation. Reisolation from these lesions yielded M. oryzae. With the same methods, 45 cultivars and lines were inoculated to determine their reactions to this disease. Most of the cultivars grown in the southern United States were moderately susceptible or susceptible to white leaf streak. Foreign cultivars tested, including BR-7, BR-11, Cica-4, Cica-6, Cica-7. Cica-8, Cica-9, Oryzica llanos, Rax clear, Teqing, and Tetep, were resistant. In 1997, the disease was found prevalent on many cultivars grown at the Rice Research Station, Crowley, LA. As symptoms of both white leaf streak and narrow brown leaf spot were sometimes observed on the same leaf; it is possible that the disease has been present, but not identified as a separate disease because of the similarity of the symptoms of the two diseases. A thorough survey is necessary to determine the extent of its occurrence and further studies are necessary to determine its yield loss potential. At present it appears to be a minor problem for Louisiana rice. White leaf streak has previously been recorded from Papua New Guinea on cultivated Oryza sativa, and from the Solomon Islands, Sabah, Nizeria, and Sierra Leone on cultivated O. glabberima Steudel and on wild perennial rice O. berthii A. Chev. (2). This is the first report of white leaf streak on cultivated rice in the United States. References: (1) F. C. Deighton. Mycol. Pap., CMI 144:1,1979. (2) F. C. Deighton and D. Shaw. Trans. Br. Mycol. Soc. 43: 515, 1960. (3) B. C. Sutton and A. K. M. Shahjahan. Nova Hedwigia 25:197, 1981.
‘Della‐2’ (Reg. No. CV‐140, PI 665400) is an aromatic long‐grain cultivar with good grain yield, good milling yields, and excellent grain appearance. It was developed with the modified pedigree selection at the Rice Research Station, Louisiana State University Agricultural Center near Crowley, LA. Della‐2 was approved for official release in December 2011 by the director of Louisiana Agricultural Experiment Station because of its enhanced yield potential and grain‐quality characteristics suitable for the aromatic specialty market. In 10 statewide trials conducted at six Louisiana locations, the average main crop yields of Della‐2, ‘Dellrose’, and ‘Cheniere’ were 7.51, 6.60, and 8.27 t ha −1 . In Uniform Regional Rice Nursery trials performed in 2008 in Louisiana, Arkansas, Mississippi, Missouri, and Texas, Della‐2 yielded an average of 9.81 t ha −1 , which was significantly higher than the 7.31 t ha −1 of Dellrose but only numerically higher than 9.35 t ha −1 of the nonaromatic check Cheniere. In 34 replicated trials where milling yields were evaluated, the average head and total rice yields of Della‐2 were 600 and 690 g kg −1 compared with 637 and 722 g kg −1 for Dellrose and 613 and 717 g kg −1 for Cheniere. The average amylose content of Della‐2 was 21.8% compared with 23.1 and 24.0% for Dellrose and Cheniere. The average alkali spread value of Della‐2, Dellrose, and Cheniere was 4.1, 4.1, and 4.4. The average 2‐acetyl‐pyrroline content of Della‐2 was 787 ng g −1 , which was higher than the 582 ng g −1 of Dellrose. Della‐2 is susceptible to sheath blight [caused by Thanatephorus cucumeris (A.B. Frank) Donk (anamorph: Rhizoctonia solani Kühn)], bacterial panicle blight (caused by Burkholderia glumae ), and the physiological disorder straighthead but moderately resistant to blast [caused by Magnaporthe grisea (Hebert) Barr (anamorph Pyricularia grisea Sacc.)]. Della‐2 is adapted to southern U.S. environmental conditions, and its improved yield potential will benefit specialty rice growers by improving their profitability.
