Head Rot of Sunflower Caused by Rhizopus oryzae in New Mexico.

Head rot was found in cultivated sunflower (Helianthus annuus) in eastern New Mexico in Tucumcari in 2007 and Clovis in 2007 and 2009 and in south-central New Mexico near Las Cruces in 2009. The disease was also observed in wild sunflower near Clovis in 2008. Disease incidence was 10 to 40% in cultivated sunflower and ~30% in wild sunflower. Heads were brown to dark brown with discoloration extending down the sepals and peduncles into the stems. The basal parts of the heads were shredded and had grayish, fluffy mycelial mats visible in the lumen, and kernels were mostly seedless. Three to five diseased heads were collected from cultivated sunflower in 2007 and 2009 and wild sunflower in 2008. Plant tissues from heads and peduncles were surface sterilized for 3 min in 0.5% NaOCl, rinsed once in sterile distilled water, cut into 0.5-cm pieces, and plated on acidified potato dextrose agar (PDA). Within 3 to 7 days, mycelial colonies with abundant aerial growth and black sporangia emerged and were identified as Rhizopus oryzae on the basis of the presence of pale brown sporangiospores with bluish stripes (3) and mycelial growth at 36°C on PDA (1). PCR amplification of the internal transcribed spacer (ITS) region of rDNA from two isolates, one from cultivated and one from wild sunflower, using primer pair ITS4/ITS5 (1) was followed by sequencing and showed a 99% homology with the sequence of the ITS region of rDNA from R. oryzae (GenBank No. FJ654430). Each isolate was tested for pathogenicity on inflorescences (5 to 6 cm in diameter) of sunflower cvs. Hysun 511 and Triumph 820 HO grown for 4 to 5 weeks in a growth chamber at 26°C with a 14-h photoperiod. To obtain inoculum, a sterile toothpick was passed through a culture of R. oryzae until a ~3-mm mycelial mat was collected at the tip. The toothpick was dabbed into the center of an inflorescence or into the peduncle. A cotton boll was placed over the inoculation and sprayed with sterile distilled water. Control inflorescences were dabbed with toothpicks with no mycelium mat. Each inoculated and noninoculated inflorescence was covered with a plastic bag that was sealed around the peduncle. Plants were kept in the growth chamber for 3 weeks. In each of two experiments, 13 plants were used per cultivar and inoculation type, with 5 plants inoculated per isolate, and 3 control plants. Symptoms observed on inoculated sunflower were similar to those on field infected sunflower. There was no difference between the two cultivars. On inoculated inflorescences, dark discoloration developed at the inoculation site and expanded over the inflorescences, and grayish mycelium with black sporangia was observed within 2 weeks. On inoculated peduncles, dark discoloration was also observed extending down the peduncle and up into the inflorescences. R. oryzae was reisolated from all inoculated heads. To our knowledge, this is the first report of R. oryzae causing head rot on sunflower in New Mexico. It is unknown what factors lead to head rot outbreaks. This disease has been reported in other U.S. regions and has been demonstrated to reduce sunflower yield and quality (2). The potential negative impact from Rhizopus head rot should be considered when determining whether to expand cultivation of this crop. References: (1) G.-Y. Liou et al. Mycol. Res. 111:196, 2007. (2) C. E. Rogers et al. Plant Dis. Rep. 62:769, 1978. (3) T. Watanabe. Pictorial Atlas of Soil and Seed Fungi: Morphologies of Cultured Fungi and Key to Species. CRC Press, Boca Raton, FL, 2002.

Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism.

A winter grazing/feedlot performance experiment repeated over 2 yr (Exp. 1) and a metabolism experiment (Exp. 2) were conducted to evaluate effects of grazing dormant native range or irrigated winter wheat pasture on subsequent intake, feedlot performance, carcass characteristics, total-tract digestion of nutrients, and ruminal digesta kinetics in beef cattle. In Exp. 1, 30 (yr 1) or 67 (yr 2) English crossbred steers that had previously grazed native range (n = 38) or winter wheat (n = 59) for approximately 180 d were allotted randomly within previous treatment to feedlot pens (yr 1 native range = three pens [seven steers/pen], winter wheat = two pens [eight steers/pen]; yr 2 native range = three pens [eight steers/pen], winter wheat = four pens [10 or 11 steers/pen]). As expected, winter wheat steers had greater (P < 0.01) ADG while grazing than did native range steers. In contrast, feedlot ADG and gain efficiency were greater (P < 0.02) for native range steers than for winter wheat steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for winter wheat steers than for native range steers. In contrast, 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ among treatments. In Exp. 2, eight ruminally cannulated steers that had previously grazed winter wheat (n = 4; initial BW = 407 +/- 12 kg) or native range (n = 4; initial BW = 293 +/- 23 kg) were used to determine intake, digesta kinetics, and total-tract digestion while being adapted to a 90% concentrate diet. The adaptation and diets used in Exp. 2 were consistent with those used in Exp. 1 and consisted of 70, 75, 80, and 85% concentrate diets, each fed for 5 d. As was similar for intact steers, restricted growth of cannulated native range steers during the winter grazing phase resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) compared with winter wheat steers. In addition, ruminal fill (P < 0.01) and total-tract OM digestibility (P < 0.02) were greater for native range than for winter wheat steers across the adaptation period. Greater digestibility by native range steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by native range steers in the feedlot, grazing winter wheat before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit.

Induction of tall fescue toxicosis in heat-stressed cattle and its alleviation with thiamin.

Livestock grazing endophyte (Acremonium coenophialum)-infected tall fescue (Festuca arundinacea Schreb. cv. Kentucky 31) at high ambient temperatures may suffer from fescue toxicosis. Adult Angus cows (Bos taurus) were fed 0 to 1 kg/d of 70% infected tall fescue seed containing about 4.4 g of loline alkaloids in factorial combination with thiamin at 0 or 1 g/d. Cows assigned to the zero level of tall fescue seed received a supplement of equivalent energy and protein. Ingestive behavior was measured at 1330 to 1430 EDT during two 4-d periods in two consecutive weeks in August on alfalfa (Medicago sativa L.) pastures using a tethered grazing system. Alfalfa intake per measured grazing session of cows given tall fescue seed declined linearly (P less than .01) as air temperatures during grazing increased above 25 degrees C, largely because of shorter grazing meals. Thiamin increased alfalfa intake per measured grazing session by extending grazing time. Alkaloids in ingested endophyte-infected tall fescue induce thiamin deficiencies in cattle that result in symptoms of tall fescue toxicosis.

Thiamin supplementation and the ingestive behavior of beef cattle grazing endophyte-infected tall fescue.

Livestock grazing endophyte (Acremonium coenophialum Morgan-Jones and Gams)-infected tall fescue (Festuca arundinacea Schreb.) perform poorly due to tall fescue toxicosis, especially when animals are under heat stress. In order to determine whether thiamin promotes recovery from tall fescue toxicosis, 1 or 0 g of thiamin per day, as mononitrate, was fed orally to adult Angus (Bos taurus) cows (380 +/- 8 kg) grazing either tall fescue pasture with and without endophyte or alfalfa (Medicago sativa L.). A tethered grazing system employing a split-plot design was used to estimate intake and components of ingestive behavior. No significant differences attributable to thiamin supplements were seen in rates of intake and biting, grazing time and intake per bite when cows grazed endophyte-infected tall fescue during the first 4 d of exposure. When cows grazed endophyte-infected (greater than 95%) tall fescue with 2,091 micrograms/g loline alkaloids after 4 d of exposure, the untreated animals ingested herbage dry matter (DM) at 1.19 kg/h, whereas the cows receiving thiamin ate 1.57 kg/h (P less than .05). Cattle achieved these rates of DM intake by forming bites of 1.0 and 1.2 g DM at 24 and 26 bites/min when treated with 0 and 1 g of thiamin per day, respectively. Thiamin supplements had no effect on ingestive behavior of cows grazing endophyte-free tall fescue or alfalfa after exposure to these forages for 4 d. Responses to thiamin generally were greater when cattle grazing endophyte-infected tall fescue were exposed to heat stress. Oral thiamin supplementation may alleviate tall fescue toxicosis of beef cattle during warm weather.