Resistant cultivars answer to Stip disorder in peppers

Resistant cultivars answer to Stip disorder in peppers

Stip disorder is officially found in New Mexico and Arizona-grown chile peppers. Stip disorder could be tied to a physiological disorder possibly combined with abiotic stress factors including hot temperatures. Stip may be linked to a calcium imbalance or deficiency – perhaps a different expression of a calcium imbalance. In the U.S., Stip disorder was found in Texas in 1975 and in California and Florida in the mid 1990s.

Peppers are a spicy, delicious vegetable, but a problem called Stip disorder which damages some pods is causing heartburn for some Southwestern producers and processors.

“Stip disorder is likely caused by a physiological disorder possibly combined with abiotic stress factors including hot temperatures,” says Mark Uchanski, vegetable physiologist with New Mexico State University (NMSU) in Las Cruces.

There are reports of Stip disorder as early as 1975 in Texas. The disorder was first reported and studied in California and Florida-grown peppers around 1995. The disorder was officially declared in New Mexico and Arizona chile pepper fields more recently.

Researchers and producers as far away as Australia and Israel have published studies describing the problem.

Uchanski used his speaking slot during the 2012 New Mexico Chile Conference in Las Cruces to issue the formal Stip disorder announcement to the attending 275 New Mexico and Arizona pepper growers, processors, and industry representatives.

Uchanski asked for a show of hands of those who had seen Stip-like symptoms on farms or at processing facilities. A few hands were raised. Uchanski then displayed a series of ugly Stip-infected chile photos in a PowerPoint visually illustrating the malady. He asked for another show of hands. More hands were elevated.

Chile peppers are a valuable cash commodity and New Mexico’s signature crop. In the state, Stip is more often found in green chile, infrequently in red chile, and so far not detected in paprika peppers.

“We don’t have exact numbers on financial losses due to Stip disorder in New Mexico and Arizona,” Uchanski told the group. “I have heard of pepper loads rejected at the processor due to this problem.”

Chile producers in New Mexico and Arizona have suspected Stip disorder since 2007 during the hotter summer months.

New Mexico is the nation’s top pungent chile pepper producer with 10,800 harvested acres; followed by California - 5,800 acres, Texas - 4,500 acres, and Arizona – 3,600 acres; all 2007 National Agricultural Statistics Service Census of Agriculture figures.

Initial visual signs of Stip include a hazy, orange-red area inside the pepper pod. Later symptoms include depressed, oval dark-brown or black spots (lesions) one-quarter to one-half inch in diameter. The lesions move toward the pod exterior. A cut open pod with Stip reveals a layer of dead cells.

“The interior of the infected pod interior appears smashed similar to an accordion,” Uchanski said. “It’s similar to when an apple is cut open and the fruit browns quickly - so does the chile pepper.”

Symptoms worsen during the ripening and post-harvest periods. The brown tissue rarely moves to the pod cuticle (waxy outer layer). Secondary decay organisms are absent in fresh pods. There are no foliar symptoms with the disorder.

Uchanski says microscopic analyses of infected pods have clusters of collapsed (dead) cells. The browning is caused by the release of tissue cell contents combined with oxidation. 

There is no sign of a puncture wound from insects or infection. The finger is sometimes pointed at stink bugs which Uchanski called a highly unlikely culprit.

California and Florida have gained a great deal of knowledge about Stip disorder since it was first found about 17 years ago.

Stip likely widespread

Until Uchanski’s chile conference announcement, Stip was considered a minor problem in New Mexico and Arizona. Uchanski’s announcement suggests otherwise – it is likely a larger and more widespread problem than originally thought.

Stip is a German word for ‘specks.’ A German paper in 1892 linked a calcium deficiency in apples to Stip. Others believe Stip is the result of plant transpiration problems tied to water loss inside the plant which can result in calcium problems.

“We deal with a lot of those situations in the Southwest. Stip is likely tied to a calcium imbalance or deficiency. Stip may be a different expression of a calcium imbalance,” Uchanski explained.

Tim Hartz, University of California-Davis Extension specialist, Davis, Calif., says Stip disorder has been found in bell peppers in California. Hartz and Uchanski agree the most progressive way to find a solution to Stip is through cultivar selection.

Hartz said the California Pepper Commission funded research on Stip in bell peppers in the late 1990s with several important findings which Hartz summarized:

  • Bell pepper cultivars vary greatly in susceptibility to Stip.
  • Stip is generally considered a calcium disorder. This problem is usually most severe under conditions that limit crop transpiration and more so with fruit maturing in fall conditions rather than summer conditions.
  • High nitrogen fertilization tends to increase Stip, but environmental conditions appear to be more important than nitrogen status.
  • Soil-applied calcium tends to be ineffective.
  • Repeated foliar calcium applications may help reduce symptoms, but the approach may not be logistically or economically feasible.

“The bottom line is that Stip is a sporadic but potentially devastating problem,” Hartz said. “Avoidance with resistant varieties is the best course. Active management practices to control or prevent the disorder tend to be minimally effective.”

Conditions which can favor calcium deficiency in the Southwest, Uchanski says, include: high or low soil moisture; inconsistent water supplies; intense sunlight; hot temperatures; a nutritional imbalance (too much nitrogen and not enough calcium); lush, excessive vegetative growth; and high salt concentration.

Uchanski conducted focus groups with Southwest pepper growers and processors who suspected Stip disorder in chiles.

“The group reported that just harvested chiles did not have much Stip,” Uchanski told the crowd. “Once in the bin, affected peppers can take a turn for the worse within 24 hours.”

Severe observations of Stip were first noticed in this region about five years ago. There is no accurate figure on total pepper crop loss in New Mexico and Arizona from the disorder.

Stip disorder is sometimes confused with blossom end rot (BER) disease found in chile. Uchanski says BER is not the cause in this case.

ER is a non-infectious disorder caused by calcium deficiency in the pepper pod. Under hot summer conditions, calcium travels with water through the plant, roots, stems, and leaves. The calcium fails to accumulate in the waxy pods.

Several theories exist for Stip causes, Uchanski says, including toxic levels of calcium which can puncture cells leading to brown spots, an unidentified pathogen, and an increase in pesticide applications; particularly nicotine-based products.

The prevailing theory, Uchanski says, is an interaction between extreme summer temperatures and some cultivars.

Uchanski dissected more than 100 years of weather data from the National Climatic Data Center (NCDC). For the Las Cruces area (NCDC Region 8), slight temperature increases have occurred in the region over the last century but no extraordinary, long-term heat changes.

To gain further knowledge about Stip, Uchanski last year called in the “SWAT” team – NMSU’s Soil, Water, and Agricultural Testing Laboratory. Uchanski provided the lab with plants with and without Stip disorder symptoms. The findings indicated symptomatic pods had higher calcium content than asymptomatic pods.

What happens next? Reliable testing protocols could be developed along with in-field cultivar screening under southwestern growing conditions.

“We could evaluate existing cultivars for resistance or susceptibility and go from there,” Uchanski summarized. “It’s a discussion we need to have from a plant breeding perspective and determine the severity of the problem in this region.”

Sponsors of the chile conference included the Chile Pepper Institute, New Mexico State University, and the New Mexico Chile Association.

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