Chile pepper (Capsicum annuum L.) is a vegetable crop of great economic importance in the southwestern United States. Major states producing chile pepper (nonbell type) are New Mexico, California, Texas, and Arizona. In 2006, chile pepper production in New Mexico accounted for ≈41% of U.S. chile production with a value of ≈102 million dollars (USDA-NASS, 2007).
In New Mexico, chile pepper is produced under sprinkle, drip, and furrow irrigation. However, furrow irrigation is the most practiced irrigation method in the state (Skaggs et al., 2000). Drip irrigation is designed to supply water to plant root zone where it is most needed, thus conserving this resource. Furrow irrigation consists of flooding fields at varying intervals. Depending on soil moisture conditions, flooding may be performed at 7- to 10-d, 10- to 15-d, and 15- to 21-d intervals. After flooding events, saturated conditions may be established in soil for 3 to 7 d depending on soil types and environmental conditions. Furrow irrigation can be thought of as periodic flooding of fields.
Major constraints to chile pepper production in New Mexico are soilborne diseases, which are manifested by wilt symptoms after plant infection. Verticillium dahliae is a major soilborne fungal pathogen that causes wilt in several crops, including chile pepper (Pegg and Brady, 2002; Sanogo and Carpenter, 2006), in the United States and worldwide. Verticillium dahliae produces microsclerotia, which enable the pathogen to persist for at least 14 years in infested field soil (Wilhem, 1955). Additionally, this fungus survives in numerous weed species across many plant families (Sanogo and Clary, 2003; Woolliams, 1966). Verticillium dahliae affects the integrity of vascular tissues in the root and the stem. Plant infection by V. dahliae results in stunting, leaf chlorosis and necrosis, defoliation, vascular necrosis, wilting, and death (Pegg and Brady, 2002). After infection of pepper plants, symptoms of Verticillium wilt may appear within 3 to 6 weeks. In plants infected with V. dahliae, several physiological processes such as respiration, transpiration, and photosynthesis are affected, and therefore yield reduction may be incurred (Tomescu et al., 2000).
Verticillium dahliae and Phytophthora capsici, causal agent of Phytophthora blight, are the two most significant pathogens associated with chile pepper wilt in New Mexico (Sanogo and Carpenter, 2006). Verticillium dahliae and P. capsici may occur together in the same chile pepper production fields and in the same plants (Sanogo and Carpenter, 2006). The occurrence of both pathogens in the same fields represents a serious challenge to crop management. Previous studies on control of chile pepper wilt have shown that P. capsici could be reduced significantly by use of alternate-furrow irrigation in contrast to flood irrigation of every furrow (Biles et al., 1992) and by use of drip irrigation (Ristaino and Johnston, 1999; Xie et al., 1999). However, field observations by chile pepper producers using drip irrigation systems indicate that Verticillium wilt is increased in drip-irrigated compared with furrow-irrigated chile pepper fields. These observations were confirmed in a 3-year field survey in which Sanogo and Carpenter (2006) found that the incidence of plant infection by V. dahliae was ≈32% greater under drip irrigation than under furrow irrigation.
The cause of increased Verticillium wilt on chile pepper grown under drip irrigation relative to furrow irrigation is not known. Field notes by chile pepper producers and field surveys are observational in nature, and as such they do not provide any systematic cause-and-effect relationship to be established between irrigation and development of Verticillium wilt. There has been no systematic study to characterize chile pepper infection by V. dahliae and development of Verticillium wilt under drip and furrow irrigation systems. It is important to conduct a systematic evaluation of the effect of irrigation on Verticillium wilt on chile pepper. Such a study will be useful for crop management from at least two perspectives. First, it will provide an ecological understanding of the behavior of V. dahliae. Second, it will provide a knowledge base for designing strategies to minimize Verticillium wilt in chile pepper production fields.
The hypothesis of this study was that Verticillium wilt increases on chile pepper grown under drip irrigation compared with chile pepper grown under furrow irrigation. Experimentally, furrow irrigation and drip irrigation were represented by periodic flooding and no-flooding conditions, respectively. The objectives of this study were to assess the effects of periodic flooding and no-flooding conditions on severity of Verticillium wilt, plant growth, and spectral reflectance-based physiological indices of chile pepper.
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