Effects of Mulch and Irrigation System on Sweet Onion: II. The Epidemiology of Center Rot

Abstract

<jats:p>Mulch (black plastic, wheat straw, or bare ground) and irrigation (drip or overhead sprinkler) treatments were evaluated for their effect on center rot of onion (<jats:italic>Allium cepa</jats:italic> L.), caused by the bacterium <jats:italic>Pantoea ananatis</jats:italic>, over the course of two seasons. Irrigation type had no effect on center rot incidence or severity in either year. In contrast, center rot development was delayed by 7 to 14 days on onions grown in straw mulch or bare ground compared to those in black plastic. Straw mulch resulted in later harvest dates and was associated with reduced levels of center rot. In contrast, black plastic increased disease incidence and hastened the onset of the epidemic. The spatial distribution of disease incidence in both years indicated the presence of a primary disease gradient. At harvest, infected plants were segregated by treatment and by duration of infection [based on disease ratings taken from the time of first symptom expression (beginning at 110 to 120 days after transplanting and then every 5 to 10 days until harvest)]. Early-vs. late-infected plants had no significant effect on yield (bulb weight). However, symptom expression in terms of the number of days after planting was significantly correlated with a disease severity index. Amount of rot in bulbs from plants displaying their first symptoms only 1 to 2 days before harvest (late-season infection) was not significant from rot levels in control bulbs at harvest. However, at 4 weeks after harvest, onions from plants with late-season infections exhibited significantly more rot in storage compared to the control.</jats:p>

Pantoea ananatis: an unconventional plant pathogen

“…The recent appearances of bacterial blight and die‐back on Eucalyptus in countries that have purchased seed from South Africa suggest seed transmission (Dr. G. Nakabonge, FABI, University of Pretoria, Pretoria, South Africa, unpublished data). Similarly, outbreaks of centre rot of onions may be a result of the introduction of infested seed into new environments/countries (Gitaitis et al ., 2004; Goszczynska et al ., 2006a).…”

“…The control of white spot disease of maize in Brazil has also been achieved by applying the fungicide Mancozeb in the initial phases of disease development (Bomfeti et al ., 2007). The use of mulch and irrigation systems has been investigated for the control of centre rot of onion (Gitaitis et al ., 2004). Irrigation type had no effect on the incidence and severity of disease.…”

Managing Crop Disease through Cultural Practices

“…In southern Israel, less frequent and reduced irrigation was shown to lower the incidence of Monosporascus cannonballus on melon and to postpone plant collapse, although yields were reduced (Pivonia et al, 2004). Gitaitis et al (2004) examined the effects of a number of treatments, including irrigation, on centre rot of onion caused by the bacterium Pantoea ananatis. They found no effect of drip or overhead sprinkler irrigation on the incidence or severity of centre rot (Gitaitis et al, 2004).…”

“…Gitaitis et al (2004) examined the effects of a number of treatments, including irrigation, on centre rot of onion caused by the bacterium Pantoea ananatis. They found no effect of drip or overhead sprinkler irrigation on the incidence or severity of centre rot (Gitaitis et al, 2004). Phytophthora capsici is a serious soil-borne pathogen of pepper (Capsicum annuum L.) and causes signifi cant crop losses worldwide.…”

Incidence of bacterial diseases associated with irrigation methods on onions (Allium cepa)

“…Several studies have shown that the irrigation method influences the incidence of diseases in onions. 11,12 At the regional level, however, information is not available. The present study aimed to determine whether the irrigation method has an influence on the incidence of diseases of bacterial origin in onions cultivated in the Lower Valley of the Rio Negro.…”