Phytophthora crown rot (blight) resistance is here and looks quite promising as part of an integrated control program for this disease on peppers! In 1996, we conducted two separate studies on Phytophthora resistant cultivars: a variety trial at the Plant Science Research Farm to look at plant and fruit characteristics and yields, and a test in infested commercial fields to see how well the resistance held up under heavy disease pressure.
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All the resistant varieties produced significantly more U.S. Fancy grade fruit (unblemished, large and extra-large peppers) than the Lady Bell. The HMX2647 (now named Emerald Isle and commercially available) had very nice fruit, slightly longer than wide (length to a diameter ratio of 1.2, about the same as a Bell Tower fruit). Several growers, attending a twilight meeting at the Research Farm last September, singled HMX2647 out as the best looking of the 24 varieties we grew. It comes with the added bonus of cucumber mosaic virus-resistance, an affliction that struck at least one Connecticut farm last season.
PP3135 and PP3136 also produced very nice looking fruit. Both produced fruits that were slightly "blockier" (L:D ratio 1.1) than those of HMX2647 with thicker walls. Often the market prefers a blocky shape. PP3135 is available commercially (Rogers, Rupp) for the 1997 season but has not yet been named. All three of the above-mentioned varieties produced fruit that were larger and earlier than Lady Bell. Reinger produced the most fruit in the trial. However, the walls were thin and they were probably too long (L:D ratio 1.5) for our markets.
To test
the resistance in infested commercial fields, we planted 10 plants
each of HMX2647 and Reinger alongside of the grower's standard
(nonresistant) variety at five different sites. All plots were
located in fumigated, mulched, raised beds and were cared for
by the individual growers using their normal practices. Unfortunately,
we did not receive enough seed of the two Roger's varieties to
include them in this study. All of the plots were located on a
slight slope just out of a "wet hole" where water tends
to pool after heavy rains. Field depressions where the soil stays
saturated for more than 48 hours is usually where Phytophthora
infection and epidemics begin. 1996 was a good year to conduct
this test because we had several heavy rainfalls throughout the
season, including more than 4 inches of precipitation during Hurricane
Bertha, July 13 and 14.
Phytophthora blight killed 46% of the grower's nonresistant standard plants in the plots by July 23, and 92% by August 27. Only 2% and 4% (1 or 2 out of 50) of the resistant plants died by August 27, demonstrating an impressive degree of resistance to the crown (stem) rot phase of the disease under severe conditions. At one of the sites, the grower's plants were dead for 20 feet in all directions around the plot of healthy resistant plants! In each study, there were similar (low) levels of branch and fruit (aerial) infections among both resistant and standard varieties.
Unfortunately, we will have to wait a while before a bacterial leaf spot/Phytophthora resistant pepper plant is developed. Until then, we recommend that all pepper producers use BLS resistant plants unless you have no choice but to plant into a field highly infested with Phytophthora, or absolutely have to follow a vine crop in rotation - then choose Phytophthora resistance. Back to back solanaceous/cucurbit crop rotations are not recommended as both plant families are preferred hosts for Phytophthora capsici. No one yet knows if these new Phytophthora-resistant varieties will eventually succumb to the disease if we allow the pathogen to continue to accumulate to ever higher levels in the soil. The best way to protect your long-term profitability is to continue to practice an integrated disease management strategy that includes; proper crop rotations and site selection, good cultural and sanitary practices, hot-water seed treatment, resistant varieties, weekly scouting and chemical controls, if necessary.
Jude Boucher, Vegetable Crops, IPM Program Coordinator
Gianna Nixon, IPM Program Assistant, University of Connecticut
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