Citrus Roots Research Articles

Identification and Quantification of Phenolics in the Leaves and Roots of Healthy and Exocortis-Infected Citrus

Identification and Quantification of Phenolics in the Leaves and Roots of Healthy and Exocortis-Infected Citrus

Soil and root copper. Evaluation of copper fertilization by analysis of soil and citrus roots

Soil and root copper. Evaluation of copper fertilization by analysis of soil and citrus roots

Aphelenchoides Goodeyi N. Sp. (Nematoda: Aphelenchoidea), a Mycophagous Nematode From South India

Aphelenchoides goodeyi n. sp. was found feeding on a culture of mixed fungi from soil around citrus roots from South India. It is distinguished by the stellate tail mucro and the short gonad. The females are probably syngonic hermaphrodite. No males were found.

Observations On the Survival of Free-Living Stages of the Citrus Nematode 1 )

Storage of free-living stages of Tylenchulus semipenetrans for 7 days at 0-30° C resulted in low mortality rates. Almost all nematodes died after 1 hour when stored at -10° C, and after 4 hours when stored at +40° C. 10° C was found to be the optimum storage temperature. Mortality after storage at 10° C for 24 months was approximately 30%, with more female larvae remaining viable than males. Infectivity of the surviving nematodes was not lower than that of nematodes extracted from fresh citrus roots. No correlation was found between seasonal fluctuations in an established nematode population and soil temperature levels.

九州の線虫相より(2)

1. Among the nematodes found in Kyushu and identified by the authors, the following are re markable from the viewpoint of nematode distribution and parasitism: (1) Pratylenchus loosi, tea root, Higashi-sonogi Town, Nagasaki Pref., (2) P. coffeae, Citrus root, Tarumizu City, Kagoshima Pref., (3) Radopholus oryzae (?), paddy field (in dry condition), Aino Town, Nagasaki Pref., (4) Tylenchorhynchus claytoni, azalea soil, Kusano Town, Kurume City, Fukuoka Pref., (5) Tylenchorhynchus sp., soybean field, Yabe Town, Kumamoto Pref., (6) Tylenchorhynchus ? sp., sugar cane soil, Okino-erabuzima, Kagoshima Pref.2. In regard to root-lesion nematodes, four species have been found in Kyushu, that is, Pratylenchus coffeae, P. vulnus, P. zeae and P. loosi.

Longevity of Radopholus Similis (Cobb) in Host-Free Soil

Burrowing nematodes do not survive more than six months in sandy soils in Central Florida (U.S.A.) in the absence of suscept roots. Populations in citrus roots and soil contained in cheesecloth, nylon, or polyethylene bags buried at depths of 31-152 cm disappeared within six months, whereas Hoplolaimus coronatus, Pratylenchus brachyurus, and numerous saprobic species survived under these conditions. Polyethylene was not toxic to burrowing nematodes, and was impenetrable to this species in greenhouse tests. Living uninfected or infected citrus roots in the vicinity of buried polyethylene bags of infested roots and soil had no effect in prolonging the longevity of the Radopholus contained in those bags. Burrowing nematodes in soil and roots enclosed in polyethylene failed to survive when stored six months at an average laboratory temperature of 24.4° C. and an average refrigerator temperature of 1.1° C. Additional bags of infested material placed in gallon cans of autoclaved soil and held six months at an average greenhouse temperature of 24.9° C. likewise failed to yield burrowing nematodes when the cans were either kept dry, maintained at field capacity, or placed on an alternating cycle from field capacity to dry conditions.

Fungi and Nematodes in South African Citrus Orchard Soils in Relation to the Citrus Replant Problem

AbstractTrichoderma viride, Aspergillus fumigatus, Penicillium javanicum, P. decumbens, and P. lilacinum constituted dominant fungus species in South African virgin soils which were present in much smaller numbers in adjacent citrus soils. The most dominant forms in old citrus soils were Fusarium solani, Fusarium spp. including F. oxysporum, Penicillium chermesinum, Pullularia pullulans, and Pyrenochaeta sp. Aspergillus niger, Mucor spp. and many others were present in about equal abundance in both old citrus and virgin soils. Phytophthora species were isolated from about a third of the old citrus soils but were not found in virgin soils. The citrus root nematode, Tylenchulus semipenetrans, was found in all but one of the old citrus soils examined but was not detected in the virgin soils. Nematodes isolated from both type soils included Trichodorus sp., Xiphinema sp., Rotylenchus sp., and numerous saprophytic species. Helicotylenchus sp. was noted in virgin soil only. The magnitude of the citrus replant problem in South Africa varied greatly but, in general, appeared to be less severe in well‐drained acid sandy soils containing relatively large numbers of the fungus, Trichoderma viride.

An Aceto-Osmium Method for Demonstrating Nematodes in Citrus Roots

Difficulties are encountered in observing nematodes in citrus feeder roots because of the presence of suberin and other unsaturated compounds. To obviate these difficulties, infected citrus roots, either fresh or preserved, are immersed in a covered jar for 2 hr at 52° C in a solution composed of distilled water, 16 parts; 10% acetic acid, 10 parts; and 2% aqueous osmium tetroxide, 2 parts. The stained, blackened roots are washed in running water for at least 1 hr and then bleached in 10-30% hydrogen peroxide at 32°C for a few seconds until the color of the roots lightens perceptibly. After several washings in water to stop the oxidation reaction, roots are dehydrated in 70, 95, and absolute ethanol held at 52 °C for 30 min at each concentration. After dehydration, roots are cleared in methyl salicylate at 52°C. Examination for nematodes in most cases, can be made after 30 min.

Heavy-Metal Accumulation by Citrus Roots

1. Various short-term experiments on the accumulation of heavy-metal ions by citrus roots are described. 2. Copper, zinc, iron, and manganese appear to be accumulated by roots from mildly acidic solutions through nonvital processes. Thus in matched samples of seedlings, half of which had the roots killed in boiling water, accumulation of these metals was essentially identical. 3. For some unknown reason, roots first allowed to adsorb Zn, Mn, or Fe were then found to adsorb more Cu than roots without this pretreatment. The other metals were not similarly affected when the order of adsorption was reversed. At the relatively low levels of saturation obtaining in these experiments, the adsorption of Cu, Zn, or Mn did not displace an appreciable amount of a previously adsorbed metal, but Cu was displaced by Fe, particularly when the latter was supplied as a chelated complex molecule. 4. In short-term tests there was little evidence that an adsorbed metallic ion repressed the adsorption of a second metal. Such repressive action was apparent, however, when two or more elements were in the same solution. Chelated Fe was particularly effective in reducing Cu adsorption. Copper, in turn, interfered somewhat with Mn adsorption. 5. Copper accumulation by citrus roots appears to be directly related to the nonreplaceable protein nitrogen of the root. 6. Color reactions showed that the bulk of the cortex is involved in the accumulation of these elements. The innermost layer, the endodermis, appeared to have the highest concentration of both Cu and Zn. 7. Apparently, the mechanism involved in the adsorption of these elements by plant roots is not entirely dissimilar to that of soil colloids where cations are held by polar linkages.

ABSORPTION OF WATER THROUGH SUBERIZED ROOTS OF TREES

It is generally assumed that absorption of water and solutes by plant roots occurs principally in the unsuberized region back of the root cap where root hairs are usually produced. It seems probable, however, that under some conditions considerable absorption must occur through the suberized regions of roots, especially those of woody plants. For example, root elongation of most trees and shrubs almost or entirely ceases in cold or dry soil, and few or no unsuberized root tips exist at such times. Nevertheless many evergreen species such as pine, privet, holly and citrus lose considerable water by transpiration during such periods. The water lost during periods of little or no root elongation presumably is replaced by absorption through the suberized surfaces of fully differentiated, mature roots. Several investigators have presented indirect evidence that this actually occurs. Crider (5) reported absorption of nitrate and phosphate through roots of citrus and vitis after all root tips had been removed and the cut ends sealed. Chapman and Parker (2) observed absorption of nitrate by orange roots which had turned brown and were at least partially suberized. Colby (4) stated that apparently apple trees can absorb enough water through suberized roots to prevent wilting but not enough for shoot growth. Nightingale (7) found that potted apple and peach trees grown at soil temperatures of 45 and 95? F. produced no new roots and some of the old roots even died at 95? F. Nevertheless these trees absorbed water as indicated by the fact that they leafed out and made some shoot growth. Whatever absorption occurred during these experiments must have been through the old suberized roots, or even, in some instances, through dead roots. In spite of the strong presumptive evidence little direct evidence of water intake through suberized roots has been obtained. In fact the only direct measurements known to this writer are those made by Hayward, Blair, and Sk alino (6) under laboratory conditions on roots of sour orange seedlings. It was decided therefore to make a series of measurements of absorption through suberized roots of trees, especially pines, growing in the open.

Device for Measuring Entry of Water into Roots

1. A potometric device for the quantitative determination of water movement into roots is described. The apparatus is designed so that it may be attached to any part of the root. 2. Experiments with young roots of corn indicate that the rate of water entry increases from the zone proximal to the root cap to a maximum at a point 10 cm. from the root tip. In most cases the rate decreases above this level in roots more than 10 cm. in length. 3. The lateral entry of water into older portions of Citrus roots is measurable, and ``they probably provide the major avenue of ingress during certain seasons of the year. The root lenticels may be the structures through which water most readily enters older portions of the root.

Pythiaceous fungi on citrus

Abstract does not appear. First page follows. Pythiaceous fungi on citrus in California were investigated during the season 1939-40. In the course of this investigation, citrus roots were examined for the presence of fungi, inoculation experiments were performed on citrus fruits with pythiaceous fungi from citrus in general, and growth-temperature relations of Phytophthora species found on citrus were studied. This paper reports the results of this work, and includes a compilation of records on the geographic distribution of Phytophthora on citrus and a description of all Phytophthora and Pythium species recorded on citrus. Pythiaceous Fungi on Roots of Citrus In previously reported work on the isolation of fungi from roots of citrus, Fawcett (3)4 states that species of Pythium and Phytophthora have been found to be associated with the damping-off and death of young citrus trees. Weindling (11) isolated Phytophthora parasitica Dastur and Pytihium spp. from citrus seedlings affected with this disease in California, and Perlberger (5) found Phytophthora citrophthora (Sm. and Sm.) Leonian and Phytophthora parasitica in the same connection in Palestine. Fawcett (1) recorded the finding of Phytophthora citrophthora and Phytophthora parasiiica in 1923 on large citrus roots and showed that the former would attack small roots of lemon trees. He (2), (3) also found Pythium megasperma Drechsl. on the fibrous roots of orange trees dying back in heavy clay soil in Tulare County, California. In 1935, Petri (6) found Pythium meqalacantlvus de Bary and Pythium de Baryanum Hesse associated with root rot of oranges in Catania, Italy.