A Crop Variety May Resist a Disease but May not be Desired by Consumers.

Blight on stems

Blight lesions on chickpea stems

The planting of disease-resistant varieties is often promoted as an alternative to the use of fungicides. If a plant variety is produced through traditional crop breeding and is able to somehow resist penetration and infection by fungi, then fungicides are not needed. Right? The problem is that when new varieties are produced through crop breeding, they often lose quality traits that are desired by consumers. In Turkey, the best quality chickpeas are susceptible to blights and require fungicide treatments in contrast to the lower quality resistant chickpea varieties.

“Chickpea is one of the most extensively grown legume crops in Turkey, the area and production being 622,214 ha and 548,000 tons, respectively. Chickpea blight, is one of the most important diseases affecting this crop wherever it is grown. The disease, which originates from infected seeds and diseased plant debris remaining in the field, mainly affects all the above-ground parts of the plants, causing lesions mostly on stems and stem breakage. Chickpea blight can be effectively controlled by using tolerant or resistant cultivars, but none of them has good quality or sells for high prices in Turkey; unfortunately, high-value cultivars are susceptible to the disease. Seed transmission is especially important where crop rotation is practiced. For this reason, effective chemical control is needed for seed and foliage treatments.”

Authors: Demirci, F., et al.
Affiliation: Department of Plant Protection, Ankara University, Turkey
Title: In vitro and in vivo effects of some fungicides against the chickpea blight pathogen, Ascochyta rabiei.
Source: Journal of Phytopathology. 2003. 151:519-524.

Crop Breeding Failure Led to Increase in Fungicides in CA Spinach Fields

The breeding of crop varieties that are resistant to pest organisms is often touted as an effective means of replacing pesticide use. And yet, pest organisms mutate and overcome the plant’s resistance. According to the California Department of Pesticide Regulation, fungicide use in California spinach fields has doubled in the last decade. The reason for the increase has been the breakdown of the plant’s resistance to mildew (Peronospora farinosa f. sp. spinaciae).

“Downy mildew disease is the most important disease problem facing the extensive spinach industry in California. … While downy mildew has been around California spinach fields for decades, the last few years have seen the development of four or five new races. Each new race potentially overcomes the resistance factors in the cultivars being planted at that time, leaving the crop susceptible to severe damage.”

“Integrated management steps must be used. … Resistant cultivars will remain a foundational piece of such a program. Judicious use of effective fungicides will remain important.”

Authors: Steven Koike and Jim Correll
Affiliation: University of California and University of Arkansas, respectively
Title: Spinach Downy Mildew: Outlining the Challenges.
Publication: Crop Notes (University of California Cooperative Extension)