A plant disease is responsible for modifying ancient agricultural practices

The chickpea (Cicer arietinum), also known as the garbanzo bean, is an annual grain legume and is a staple crop and important source of protein in central Asia, Africa, India and the Mediterranean. It also is one the eight Neolithic founder crops thought to be responsible for the origins of agriculture, and was first domesticated by early farming communities in a region of the Near East, known as the Fertile Crescent.

The eight founder crops are composed of three cereals (einkorn wheat, emmer wheat and barley); four legumes (lentil, pea, chickpea and bitter vetch); and one oil and fiber crop (flax or linseed). Chickpea is the only one of these crops that is planted in the spring. The others follow the set pattern of fall sowing and harvesting in early summer. This cycle shift is now assumed to be due almost exclusively to a single plant disease—Ascochyta blight.

Ascochyta blight

Asochyta blight is fungal disease caused by Didymella rabiei (formally Ascochyta rabiei) and is considered to be the most serious disease affecting chickpeas wherever they are grown. It can affect leaves, stems and pods and, under optimal environmental conditions, it can spread among and throughout fields rapidly, causing substantial losses. This disease is enhanced by cool temperatures (65-70 degrees F) with high humidity, and/or some form of water splashing (rainfall or thunderstorms). These environmental conditions are common over the winter in the Near East, where most of the rainfall occurs between December and February.

Chickpea domestication

The chickpea is thought to have been domesticated from the wild form C. reticulatum—a relatively rare plant native to southeastern Turkey—about 11,000 years ago. The domesticated form is now planted during spring for summer harvest. It is also well-known today that a fall-planted crop will routinely yield up to 1-1.5 tons per acre more than spring-planted crops.

Therefore, cropping over the winter should be the practice of choice, but it is not, and this has been the practice for thousands of years. Why did ancient farmers stop planting in the fall despite its obvious agronomic benefits? There must have been a good reason for changing this practice and sacrificing high yield potential for the much lower and unstable yields obtained with a system planted in spring.

Question answered

This question was answered after experiments were conducted in the early 1960s by a group in Israel, clearly implicating the disease Ascochyta blight as the major yield-inhibiting factor. Those trials planted in the fall were destroyed by the disease in spring. Spring-sown crops were able to better avoid the disease but yielded much less (less than 1.0 tons per acre).

They additionally noted that several partially disease-tolerant lines planted in fall produced 70 percent more seed yield than the spring-planted crops, while disease-susceptible crops planted in fall yielded nothing. Therefore they concluded that the disease was the primary reason for modification of planting date for the crop.

Conclusions

Archeological records from the Fertile Crescent areas also support this concept of chickpea production being abandoned as a field crop for a period of about 3,000 years. There is evidence suggesting that chickpea production began at the end of the pre-pottery Neolithic age (9,000 to 10,000 years ago), suddenly vanished and then reappeared in the early Bronze Age (6,000 years ago) after farming began.

The problems encountered with growing the crop over the winter due to this plant disease seemingly explain why it was not detected from the archeological records during that gap period and that the conversion of planting chickpeas to the spring must have started after the initiation of farming (Bronze Age).