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Blackhawk arrowleaf clover released by Texas A&M AgriLife Research


New clover has multiple disease resistance


By Robert Burns


Texas A&M AgriLife Research recently released Blackhawk, a new arrowleaf clover promising high forage production with improved disease resistance.

Dr. Gerald Smith, Texas A&M AgriLife Research forage breeder, said he developed Blackhawk from lines with natural resistance to the fungal soil pathogen Pythium ultimum and for tolerance to bean yellow mosaic virus. 

Developed at the Texas A&M AgriLife Research and Extension Center at Overton, Blackhawk traces its lineage back to dark-seeded lines from 1984 field selections of arrowleaf cultivars Yuchi, Amclo and Meechee, Smith said.

Soil pathogens such as Pythium ultimum kill or damage germinating seed and emerging arrowleaf clover seedlings, Smith said. Both Apache and Yuchi arrowleaf clover are susceptible to this seedling disease, and in laboratory trials, inoculation with the disease resulted in 100 and 73 percent dead or severely diseased seedlings, respectively.

“In contrast, Blackhawk is resistant to this disease, and only 33% of the seedlings showed any sign of damage due to fungal disease,” he said.

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Smith is known nationally for the development of Apache arrowleaf clover, which he released in 2001, according to Dr. Charles Long, resident director of research at the Overton center.

Clover can be an important part of forage production – and by association, cattle production – in the southern U.S., Smith said. Arrowleaf clover has long shown good production potential. If planted or overseeded into warm-season pastures in the fall, it promises grazing for cattle in early spring when warm-season grasses are dormant.

As early as the 1960s, from East Texas to Georgia, it was common practice to mix arrowleaf seed with crimson clover seed, according to Smith. By mixing the early-maturing crimson clover and late-maturing arrowleaf, ranchers and farmers could have forage from February through early June.

However, multiple disease problems, including plant viruses and fungal root diseases, effectively put a stop to the practice by the late 1980s and early 1990s, Smith said. Of the diseases, bean yellow mosaic virus was one of the most prevalent and damaging problems. The virus didn’t affect crimson clover, but either killed or stunted arrowleaf clover.

It was in response to this problem that Smith developed and released Apache arrowleaf clover in 2001. Apache became one of the most widely used arrowleaf clovers in the U.S. South, according to Smith.

In terms of tonnage of forage produced per acre, Blackhawk and Apache are very similar, Smith said. However, in addition to having natural resistance to soil pathogens that attack seedlings, Blackhawk has the additional advantage of going dormant about a week earlier than Apache. This means Blackhawk is less likely to compete with warm-season forages like Coastal or Tifton 85 Bermuda grass.

Despite the similarities, the histories of developing Blackhawk and Apache are “quite different,” he said.

“On Apache, we started with a really broad germplasm base, and we selected for a number of generations for resistance to bean yellow mosaic virus,” Smith said. “We stopped at that, and released Apache, and it’s been a great variety for us, and continues to be a great variety.

“With Blackhawk, we started at a different place. We used a large germplasm collection, but we selected initially for resistance to fungal seedling diseases. We want to get that fixed first, and then after we had resistance to those diseases, we selected for resistance to bean yellow mosaic virus. So essentially, Blackhawk has multiple disease resistance.”

Blackhawk seed is black, hence its name, Smith said. Curiously, Blackhawk’s resistance to seedling diseases is linked to seed pigmentation.
This correlation between dark-pigmentation and fungal disease resistance in legumes has long been known, he said.

“Dark-seeded genotypes show increased tolerance to fungi such as Pythium ultimum and P. irregulare, when compared to light colored seeds,” Smith said. “The protective pigments are anthocyanins, which are also found throughout plants in flowers, leaves, seed, etc.”

Blackhawk arrowleaf clover’s resistance to seedling diseases is linked to seed pigmentation. 

(Texas A&M AgriLife Research photo by Robert Burns)