Issue link: http://read.dmtmag.com/i/654468
12 MARCH 15, 2016 Good Fruit Grower www.goodfruit.com Industry needs an alternative to ubiquitous Manchurian crab apple. by Ross Courtney F or decades, apple growers have used Manchurian crab apples to pollinate their fruit. The crab apples bloom early, and Snowdrift apples bloom a little later. Between the two, orchardists figured they had their bases covered. Now, a Wenatchee, Washington, researcher says there is more to it. He is searching for new pollinizer trees to give growers more genetically precise alternatives, spe- cifically those that resist rot. "Think about the biology of your pollinizers," said Dr. Stefano Musacchi, tree fruit physiologist at Washington State University's Tree Fruit Research and Extension Center in Wenatchee. Musacchi is part of a team of researchers working under a five-year, $1.9 million grant from the U.S. Department of Agricultural Foreign Agricultural Service Technical Assistance for Specialty Crops program. The work was triggered by a 2012 international trade incident, when Chinese inspectors shut down U.S. imports for two years after they found three types of rot on a shipment of Washington apples. Musacchi's colleagues, Dr. Karen Lewis, Dr. Mark Mazzalo, Dr. Parama Sikdar and doctoral student Christian Aguilar, are looking for ways to control the rot through pruning techniques and post-harvest fumigations. Their work helped persuade Chinese authorities to reopen their ports in November 2014. At the same time, the industry must think ahead, Musacchi said. The research team is searching for long- term options for not only rot problems, but also pollen compatibility, tree shape and bloom dates. Too often, growers plant pollinizers as an after- thought, choosing what they've always used out of habit, Musacchi said. He urges them to be more discerning, making sure pollinizer trees line up with the DNA of the crop tree. For example, Manchurian crab apples have pollen that is partially incompatible with several important commercial apple varieties, such as Red Delicious, Gala and Honeycrisp. Most varieties of cultivars and pollinizers have two alleles, the genetic markers in pollen. For fertilization, alleles must be different between pollinizer and fruit flower, hence the term "cross-pollination." Working with J. Franck Schmidt and Son Nursery in Boring, Oregon, Musacchi has collected 30 genotypes of crab apples he keeps in pots in the Research and Exten- sion Center's greenhouse, though he plans to plant some in the ground at the center's Sunrise research orchard east of Wenatchee. He will tend 143 trees of each strain, crushing their leaves to find the genetic markers, and study when they bloom, the size of their fruit, the shape of the tree, resistance to disease and other characteristics. His goal is to find two to three pollinizer genotypes that best match each of the industry's main commercial cultivars. "Because everybody was using some genotype as a habit but not really with a scientific base of knowledge," Musacchi said. • Looking for new POLLINIZERS Findings show treatments before and after harvest reduce infection rates. by Ross Courtney A W a s h i n g t o n S t a t e University researcher has determined which chemi- cal fungicides work to con- trol bull's-eye rot, a fungal infection partially blamed for a two-year shutdown of apple exports to China. Christian Aguilar, a graduate student at WSU's Tree Fruit Research and Exten- sion Center in Wenatchee, Washington, has concluded that fungicide treatments both before and after harvest will reduce the rates of two strains of bull's-eye rot — Neofabraea perennans and Cryp- tosporiopsis kienholzii — most com- mon to apple growing areas in central Washington. In pre-harvest trials in 2012, 2013 and 2014, Topsin M (thiophanate-methyl) worked the best of three candidates in reducing bull's-eye rot, regardless of tim- ing. In the postharvest trials, Penbotec (pyrimethanil) and Mertect (thiabenda- zole) delivered the best results out of four candidates. Aguilar told growers at the North Cen- tral Washington Apple Day conference in late January in Wenatchee that they should treat their orchards and the fruit from those orchards postharvest if they have a history of bull's-eye rot or if they see cankers. "Most likely there will be fruit infection to follow," she said. Bull's-eye rot causes cankers that spread on tree branches and brown, firm lesions that appear in concentric rings on fruit skin. Splashing water, such as by irrigation, spreads the disease. Tree inoculation is most common in April and in fall after harvest, while fruit inocula- tion is most common in September and October. Bull's-eye rot was one of three fungal diseases found by Chinese officials in a shipment of Washington apples, prompt- ing them to shut down imports from 2012 to 2014. Aguilar is part of a team of researchers working toward solutions under a five-year $1.9 million grant from the U.S. Department of Agriculture Foreign Agricultural Service Technical Assistance for Specialty Crops program. Other researchers are examining the role of pruning and postharvest fungicides to control the other two diseases and searching for alternative pollinizers, which may be resistant to rot, to the commonly used Manchurian crab apple trees. Also, other researchers will test other chemical controls for bull's-eye in the future, Aguilar said. The search for alternate chemicals is important because Topsin-M and Mer- tect share the same mode of action, rais- ing the potential for cross resistance, she noted in her final project report. Growers are typically advised against using chemi- cals with the same mode of action both in the field and packinghouse. • Researcher is targeting bull's-eye rot Pollination COURTESY STEFANO MUSACCHI/WSU TREE FRUIT RESEARCH AND EXTENSION CENTER Tree fruit researchers are searching for new pollinizer trees as alternatives to the Manchurian crab apple, such as this one at a Boring, Oregon, nursery.. TJ MULLINAX/GOOD FRUIT GROWER A bull's-eye rot canker.