Peach Roots Research Articles

Studies On the Host-Parasite Relations of Pratylenchus Penetrans (Cobb) To Apple Seedlings

A technique is described for the inoculation, under aseptic conditions, of apple seedlings with the root lesion nematode Pratylenchus penetrans (Cobb, 1917) Filip. & Stek., 1941. Under these conditions apple feeder roots (i.e. those without secondary thickening) react to nematode invasion by a rapid discolouration of the outermost, (i.e. epidermis and hypodermis) and innermost, (i.e. inner cortex and endodermis) cortical tissues, but show little or no reaction in the intervening cortical parenchyma. This response is compared with that of peach roots, in which all the cortical tissues are readily discoloured by this nematode. Histochemical tests suggest that sensitivity to P. penetrans is correlated with the presence and concentration of phenolic substances in the various tissues of these two hosts.

(Nota n.º 4) Sôbre os nematódeos que parasitam o pessegueiro

This paper deals with galled peach roots from two localities in Brazil (Ouro Preto and Piracicaba). Both samples were found attacked by Meloidogyne incognita acrita Chitwood, 1949. The material from Piracicaba also harboured two species of dagger nematodes (Xiphinema campinense Lordello, 1951, and X. krugi Lordello, 1955).

THE PEACH REPLANT PROBLEM IN ONTARIO: VII. THE PATHOGENICITY OF PRATYLENCHUS PENETRANS (COBB, 1917) FILIP. & STEK. 1941

Experiments were carried out to determine the role of Pratylenchus penetrans (Cobb, 1917) Filip. & Stek. 1941 in the peach replant problem. It is shown that this nematode is a true plant pathogen since it invades and causes necrosis of peach roots in the absence of bacteria and fungi. Necrosis of the root tissue occurs rapidly and appears to take place in advance of the invading nematode. The main mechanism involved in the formation of the lesion is the production of phytotoxic substances through hydrolysis of the cyanophoric β-glucoside, amygdalin. P. penetrans is capable of hydrolyzing this substance in vitro. It is concluded that, although P. penetrans is the most important primary parasite and a true plant pathogen, its main role in peach replant failure appears to be its ability to incite root degeneration by providing extensive infection courts for soil microorganisms.

THE PEACH REPLANT PROBLEM IN ONTARIO: VI. THE RELATION OF PRATYLENCHUS PENETRANS TO THE GROWTH OF YOUNG PEACH TREES

Further evidence was accumulated indicating that the peach replant disease decreases in severity as the interval increases in time between removal of the old orchard and the planting of new trees. The ameliorating effect of the interval may be related to the decline of Pratylenchus penetrans (Cobb, 1917) Sher & Allen, 1953. In experiments, increased growth of peach was associated with the control of P. penetrans by nematocides and P. penelrans was found to be the first nematode to attack newly developing peach roots. The populations of P. penetrans within such roots increased rapidly, then gradually declined. Generally, ectoparasites appeared later, increased relatively slowly, and occurred infrequently until late in the second growing season. The soils of all commercial peach nurseries in Ontario contain P. penetrans and the nematode may be transported in the roots of nursery stock.

THE PEACH REPLANT PROBLEM IN ONTARIO: II TOXIC SUBSTANCES FROM MICROBIAL DECOMPOSITION PRODUCTS OF PEACH ROOT RESIDUES

Experiments were carried out to evaluate the importance of soil toxins in the peach replant problem and to determine whether the substances produced by the interaction of microorganisms occurring in old peach orchard soils and peach root residues were toxic to living peach roots. A rapid and accurate indication as to whether or not these substances were toxic was obtained by determining their effect on the respiration of excised peach root tips. It was demonstrated that substances which inhibit the respiration of excised peach root tips are produced when peach root residues, and also, chemically pure amygdalin, are acted on by certain microorganisms occurring in old peach orchard soils. Such substances were not produced when the soils were autoclaved before amygdalin was added or when other soils were used in which no breakdown of amygdalin had occurred. Again no such inhibiting substances were produced when other root residues, such as sour cherry, tobacco, or pepper roots, were added to these soils in place of peach root residues or amygdalin. The inhibiting substances were readily obtained by extraction with water and they proved to be highly active physiologic agents; the inhibiting effect on the respiration of peach root tips, which ranged from 40 to 90%, could be detected after tips had been less than half an hour in the toxic leachates. In addition to inhibiting respiration these substances also induced darkening and finally the necrosis of meristematic cells. All of these effects proved to be irreversible after tips had been five hours in the toxic leachates. The root tips were apparently killed after this time. Parallel experiments were carried out also with pure amygdalin, and similar inhibition of respiration and injurious effects on meristematic cells were obtained with microbial degradation products of either amygdalin or peach root residues. Water solutions of amygdalin, emulsin, amygdalin and emulsin combined, and various benzaldehyde dilutions were also tested. Inhibition of respiration and darkening of apical meristems were only obtained, however, in solutions where amygdalin was hydrolyzed by emulsin and in the various concentrations of benzaldehyde in water. They were not obtained in the separate solutions of either the glycoside or the enzyme. It was concluded, therefore, that microbial action on the amygdalin fraction of peach roots is mainly responsible for the toxic factor frequently encountered in old peach orchard soils.

Anatomic effects of the viruses of Pierce's disease and phony peach

Abstract does not appear. First page follows. Introduction Previous investigations have shown that in its method of transmission Pierce’s disease virus is closely associated with the xylem of the hosts (Houston et al., 1947).3 Furthermore, the external symptoms of the diseases caused by this virus—Pierce’s disease of the grape and dwarf disease of alfalfa—suggest a disturbance in the water-conducting system (Hewitt et al., 1942b); (Weimer, 1931). At present no other virus is known to be so definitely associated with the xylem as that of Pierce’s disease. A study of the pathological anatomy of the hosts of this virus is therefore of particular interest in the problem of tissue relations of viruses. The investigation reported in this study was undertaken to determine whether the anatomic symptoms occur in the xylem and to what extent, if at all, they are restricted to this tissue. An attempt was also made to determine the nature and location of the first signs of histopathological disturbances. This was done through developmental studies on infected grape seedlings and cuttings of alfalfa. Certain viruses cause degenerative changes in the xylem, without necessarily being limited to this tissue. Among these, the psorosis virus is particularly well known. The anatomy of the affected wood of citrus has been described (Fawcett and Bitancourt, 1943); (Webber and Fawcett, 1935). Phony peach virus also appears to cause disturbances in the xylem (Hutchins, 1933), but the information concerning its anatomic effects on this tissue is not available. The pathological anatomy of phony peach roots has been briefly considered in the present study in order to obtain additional information on the effect of viruses on the xylem.

Effects of Temperature on Growth, Anatomy, and Metabolism of Apple and Peach Roots

Effects of Temperature on Growth, Anatomy, and Metabolism of Apple and Peach Roots