Plant Problems [antikvár]

Introduction"The general belief has long been that if you look after yourself, then you will be less susceptible to ailments. Get your feet wet or go out in the rain and you will be more likely to catch a cold. Neglect your plant, fail to feed and water it, and It will be more likely to be affected by disease. Clubroot, however, seemed to belie this maxim."Several years ago, while engaged in research on clubroot, a particularly important plant disease, I consistently found one concept difficult to convey to some of my colleagues. The notion that I put forward was that the better growing (or the more healthy, if you hice) the plant, the more severely it was hkely to suffer once clubroot had gained a hold. This seemed to fly in the face of much of the information that their own researches with other problems had taught them; it seemed to fly in the face of much logic; and it certainly flew in the face of the advice promulgated by countless generations of mothers and nannies. However, my experience and my experiments all told me that the better growing, more vigorous plants succumbed soonest.The explanation (or at least, the explanation that satisfied me) lay in the nature of the disease and the way it reveals itself The cause of clubroot, which affects only the Brassicaceae (the cabbage family), is a curious species of fungus known as Plasmodiofhora brassicae. The symptoms of clubroot are dramatic and unmistakable: the roots are distorted to form massive andgrotesque galls, sometimes in the form of a single club-hke strucmre, sometimes in the form of finger-like sweEings that give the entire root system the appearance of dahha mbers. In consequence, the conducting and other functional tissues of the roots are distorted and fail to fiinction properly. The plant then suffers a serious reverse in its fortunes and dechnes quicidy in vigour, although, significantly, it isn't generally killed.The impressive outward manifestations of clubroot are brought about by increases in both the size and number of the root cells. Like aU tissue growth in plants and animals, this is under the control of chemicals popularly called hormones. Plants belonging to the Brassicaceae also contain chemicals that are the precursors of hormones, or of substances very like them. In ways still not understood, the presence of Plasmodiophora in the tissues causes the precursors to change to the real thing, with consequent tissue proliferation. And it's here, too, that clubroot is rather unusual; not many diseases result in an increase in the growth of at least part of the host plant (the plant being attacked). More usually, the entire plant grows less, and is smaller and enfeebled.This story demonstrates that plant pathology (the science of the study of plant diseases) contains few golden rules, and that even experts can be surprised by the behaviour of a problem with which they are personally unfamihar.Diseases are only part of the difficulties that can befall plants. Like people and animals, plants are also prey to attack by pests.