Widespread Occurrence of the Aecial Stage of Sunflower Rust Caused by Puccinia helianthi in North Dakota and Minnesota in 2008

Abstract

Sunflower rust caused by Puccinia helianthi (Schw.) is widespread in North America and occurs annually on cultivated sunflower (Helianthus annuus L.) and wild annual and perennial Helianthus spp., although severity on the U.S. sunflower crop has been increasing in recent years (2). P. helianthi is a autoecious, macrocyclic rust, but the aecial stage is rarely observed in the field (1,3,4). In most years, the earliest appearance of sunflower rust in North Dakota (ND) and surrounding states usually occurs in early August as the uredinial stage. Initial inoculum can result from urediniospores that overwinter in the Northern Great Plains, urediniospores blown in from areas south of North Dakota, or basidiospores completing the life cycle. However, aecia have been noted very infrequently and never widespread, indicating initial inoculum is usually urediniospores. Aecia of P. helianthi were first observed on 24 June 2008 in a commercial sunflower field (confection hybrid CHS 3126) near Mohall, ND. Aecia cups measuring 0.2 to 0.3 mm in diameter were observed in clusters that were 1 to 7 mm wide in diameter and containing as many as 150 cups. Aecia cups were bright orange but turned brown-black as they senesced. As many as 15 aecial clusters occurred on individual leaves or cotyledons. Aeciospores were ellipsoid, hyaline, and measured approximately 20 μm in diameter. On 4 July 2008, uredinia were first observed in the same Mohall, ND field. At that time, uredinia, aecia, and senesced aecia could all be found on the same leaves. In a non-fungicide-treated strip of the field, pustule coverage on the lower leaves was 10 to 20% by mid-July, pustule coverage on the upper four leaves of plants in the untreated strip was 56% by 27 August, and yield at harvest was less than 200 kg/ha. The rest of the field was sprayed twice with fungicides and yielded 1,571 kg/ha, which is similar to the statewide yield average of 1,573 kg/ha in 2008. To determine the prevalence of aecia in the primary growing regions of ND and Minnesota (MN), surveys were conducted in 75 sunflower fields in 18 counties between 22 and 24 July in ND and 34 fields in 8 counties between 17 and 31 July in MN. Incidence of aecia and uredinia were determined by visual observation of a minimum of 20 plants scouted in a ‘W’ pattern in the field. Rust was found in 31 and 53% of fields in ND and MN, respectively. In fields where rust was found, both aecia and uredinia were observed in 37% of the fields, aecia only in 29% of the fields, and uredinia only in 34% of the fields. Although it is uncertain why aecia were widespread in 2008, night temperatures in Mohall, ND, where aecia were first observed, reached the dew point temperature on 51 of 61 days in June and July, suggesting that dew or fog likely formed. Thus, favorable conditions for germination and infection early in the growing season indicate widespread occurrence of rust was likely a result of local inoculum sources. The early appearance of aecia is cause for concern for two reasons: significant yield loss can occur when rust appears early in the growing season; and the presence of aecia suggest that the pathogen completed its sexual cycle. When P. helianthi completes its life cycle it is likely that a greater diversity of races will result (4). References: (1) D. L. Bailey. Univ. Minn. Tech. Bull. 16:1, 1923. (2) D. Berglund. Natl. Sunflower Assoc. Online publication. /Berglund_2007_NSA_Survey_08. 2008. (3) H. S. Jackson. Mem. Torrey Bot. Club 18:1, 1931. (4) G. A. Kong et al. Australas. Plant Pathol. 28:320, 1999.

Genetic mapping of rust resistance genes in confection sunflower line HA-R6 and oilseed line RHA 397

“…Yield losses to the disease can occur in a range of environments and climatic conditions, from hot and dry climates where sunflowers are grown under pivot irrigation, such as in the US Central Great Plains (Gulya 2006;Kandel 2008Kandel , 2012 to cooler and wetter climates where sunflowers are grown in dry-land production systems such as in North and South Dakota Friskop et al 2011). Sunflowers with severe rust infection can have a significantly reduced yield (smaller head size, fewer achenes, lighter test weight, and decreased oil content) as compared to uninfected plants (Fick and Zimmer 1975;Shtienberg and Zohar 1992;Markell et al 2009). In addition, the quality of the confection seeds in severely infected fields may not meet grading standards established by the industry and desired by consumers, exacerbating the economic loss to sunflower producers.…”

Registration of Two Double Rust Resistant Germplasms, HA‐R12 and HA‐R13 for Confection Sunflower

“…Combining multiple rust resistance genes into one genotype will make for more durable and broad‐spectrum resistance. This is especially important for rust resistance because new races can be produced through both sexual and asexual means, accelerating the development of new virulence races more easily and rapidly than through mutation alone (Kong et al, 1999; Sendall et al, 2006; Markell et al, 2009).…”

Registration of Two Confection Sunflower Germplasm Lines, HA-R10 and HA-R11, Resistant to Sunflower Rust

“…is a serious disease that has been increasingly prevalent in much of the U.S. sunflower‐producing region (Gulya and Markell, 2009). Similarly, the sexual stage of the pathogen has been observed with increasing frequency, resulting in potential race changes and an earlier onset of the disease (Markell et al, 2009). Yield losses as high as 80% were recorded recently (Markell et al, 2009), and the disease can also reduce seed quality.…”

“…Similarly, the sexual stage of the pathogen has been observed with increasing frequency, resulting in potential race changes and an earlier onset of the disease (Markell et al, 2009). Yield losses as high as 80% were recorded recently (Markell et al, 2009), and the disease can also reduce seed quality. This is particularly important for the confection sunflower market, which requires a specific seed size, shape, and color for human consumption.…”