The Effects of Verticillium Wilt (Verticilli1m dahliae Kleb.) on Cotton Yield and Fiber Quality

INTRODUCTION

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Aegean cotton generally is considered to be the best quality and is preferred for its longer staple length by the local textile industry. Cotton production in Aegean Region for 2005 was 254,000 tones at 176,000 ha planting areas and lint yield was 1445 kg ha^-1 (Ozudogru and Cakaryıldırım, 2005). Cotton diseases are one of the major constraints affecting yield and quality in Aegean Region. Especially, verticillium wilt incited by the soilborne fungus Verticillium dahlie Kleb., is found in many cotton fields. Onan and Karcılıoglu (1998) reported that pathotype of pathogen is SS-4 in Aegean Region.

Weather and cultural conditions that generally favor more severe occurrences of Verticillium wilt include prolonged periods of cool, wet weather, cool weather with frequent irrigations and cultural practices (such as excessive fertilization or irrigation) that encourage rank growth and delayed maturity. Continuous cropping with less-tolerant (more susceptible) cotton varieties and less aggressive crop rotations out of cotton has been shown to sustain or even increase levels of microsclerotia. Higher surface soil levels of microsclerotia have been shown to increase the chance of severe infections with more-susceptible varieties (Hutmacher et al., 2005).

Symptoms of Verticillium wilt are easily confused with two other widespread diseases, Fusarium wilt or yellows and bacterial wilt. However, Verticillium wilt is found mostly in temperate zones and is prevalent in the northern states having relatively low soil temperatures (optimum 21°C). The disease is most severe during cool to warm weather, but not as prevalent in hot weather. It is not unusual for every plant in a badly infested field to be infected, especially where susceptible crops have been grown for many years. If weather conditions are unfavorable for Verticillium development, only a slight reduction in yield or quality may occur. The fungus produces toxins that cause tyloses or gums to form in the vascular (water-conducting) tissues, resulting in a greatly decreased flow of water from the roots to the foliage (Anonymous, 1997).

The foliar symptoms of verticillium wilt were approximately 27% for Aegean Region, 25% for Cukurova and 16% South Eastern Anatolia in Turkey. The losses of seed cotton yield due to verticillium wilt were estimated 12, 12 and 10% for Aegean Region, Cukurova and South Eastern Anatolia, respectively (Esentepe, 1979; Sezgin, 1985; Sagir and Tatli, 1995).

Bejorano-Alcazar et al. (1997) revealed that the greatest yield reduction was observed in plants showing symptoms before opening of first flowers and yield increased with delay in the development of foliar symptoms after opening of the first bolls. Incidence of verticillium wilt foliar symptoms is highly influenced by inoculum density and the virulence of V. dahlia pathotypes prevailing in soil, as well as by air and soil temperature and cultivar tolerance (Bejorano-Alcazar et al., 1995). The correlation between seed cotton yield and wilt severity was negative, while correlations between lint percentage, fiber length, fiber fineness and fiber strength with wilt severity changed by susceptibility of cultivar (Kaymak et al., 1976). Fiber quality parameters were nagatively affected by verticillium wilt in especially high yielding cultivars (Yelin and Ersan, 1985; Kechagia and Xanthpoulos, 1998; Abbasi, 1998).

The objective of this study was to determine the influence of veriticillium wilt on yield and fiber quality parameters in two different fields.

MATERIALS AND METHODS

This study was conducted at Nazilli Cotton Research Institute (latitude 37⁰44^l-37⁰49^l N and longitude 27⁰44^l-27⁰50^l E) in 2004-2005. The cotton cultivars (Gossypium hirsutum L.), Nazilli 84 S (Aegean Region standard cotton cultivar), Carmen (tolerant to verticillium wilt) and Cukurova 1518 (susceptible to verticillium wilt) were used as a material.

Cotton cultivars were planted in two different fields to test the verticillium wilt performance of cultivars. One of the fields were infected field with non-defoliating pathotype V. dahliae Kleb., 24 p/g), other was non-infected (control). The experiments were arranged as a randomized complete block design with four replications. The plots were 12 m length and consisted of four each row. In this study, 60 kg ha^-1 N and 60 kg ha^-1 P₂O₅ were applied to soils as the pre-planting fertilizer from 20-20-0, 60 kg ha^-1 N as pre-flowering fertilizer from ammonium nitrate (33%). The cultural managements such as irrigations and plant protection applicants were programmed according to recommended for Aegean Region cotton growing. Measured characteristics were seed cotton yield (kg ha^-1), lint percentage (%), fiber length (mm), fiber fineness (mic) and fiber strength (g tex^-1). Variance analysis and Fisher’s LSD mean separation tests at 0.05 probability level.