Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
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Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
Chapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ation Road, Lake Alfred. Florida 33850 USA and Department of Nematology. Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.Citrus is grown in more than 125 countries in a belt within 35° latitude north or south of the equator. The major limiting factor to citrus production is Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 a requirement that the occurrence of freezing temperatures be of very short duration. Within the family Rutaceae, the genera Citrus (oranges, mandariEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
ns, pomelos, grapefruit, lemons, limes and citrons), Fortunella (kumquats) and Pondrus (trifoliate oranges) contain the principal commercial species (Chapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ki et al.. 1986). Approximately 60% of the world’s citrus production is consumed as fresh fruits and nearly one-third of total production is used in international trade (Fortucci-Marongiu, 1988).Citrus spp. are naturally deep rooted plants (Ford. 1954ứ. b) and optimum growth requires deep, well-drai Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ned soils because roots will not grow into or remain in saturated zones. Nevertheless, trees can be well-managed in areas with high water tables if grEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
own on beds. Citrus grows well under any rainfall regime provided that adequate soil moisture can be maintained. Irrigation of citrus is commonly pracChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ity to manage soil moisture is critical for good production, particularly during the period when fruit are set after the first seasonal flower bloom (Sites et al.. 1951). There is a tendency at present in the United States and elsewhere to increase early returns by planting higher density orchards w Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ith shorter life expectancies due to such diseases as citrus blight, tristeza and greening (Hearn, 1986).Citrus NematodesNumerous nematode species areEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
associated with the citrus rhizosphere (Cohn, 1972). To date, however, relatively few have been show'n to be of economic importance. With the notableChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 cdaphic conditions or to the natural distribution of a particular nematode. Because the etiology of specific nematode diseases of citrus affects management recommendations, the recognized nematode pathogens are discussed completely in separate sections.Plant Parasitic Nematodes in Subtropical and Tr Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 opical Agriculture M. Luc, R. A. Sikora and J. Bridge (eds)©CAB International 1990321322PLANT PARASITIC NEMATODES IN SUBTROPICAL & TROPICAL AGRICULTUREbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
ETylenchulus semipenetransThe “citrus nematode," T. semipeneirans, is aptly named since it occurs in all citrus producing regions of the world and limChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 various surveys estimate that the nematode infests from 50-60% (California, Florida) to as many as 90% (Texas, Arizona) of cunent orchards. Similar statistics arc reported worldwide (Van Gundy & Meagher, 1977 ; Heald & O’Bannon, 1987).Tylenchulus semipenetrans was first detected on ciưus roots in C Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 alifornia in 1912 and named and described during the next two years (Cobb 1913, 1914). The nematode causes the disease “slow decline” of citrus. The pEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
rimary effect of T. semipeneirans in newly infested sites is a gradual reduction in tree quality so that over a period of years infested trees are smaChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ounced effects on tree growth may be noted soon after planting.SymptomsSymptom development depends on overall orchard conditions. Infested trees growing under otherwise optimum conditions may yield somewhat less fruit while appearing quite healthy. As conditions become less suitable for tree growth, Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 effects of citrus nematode parasitism are more apparent (Van Gundy & iMartin, 1961; Van Gundy ef al., 1964; Heald & O'Bannon, 1987). In new citrus plEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
antings, symptoms development progresses slowly as nematode populations develop to high levels (Cohn et al., 1965). Symptoms are those associated withChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 & Martin, 1961; Heald & O’Bannon, 1987). Wilting occurs earlier during periods of water stress and leaf drop is more pronounced producing exposed branch terminals.Heavily infected feeder roots are slightly thicker than healthy roots and have a dirty appearance due to soil particles that adhere to g Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 elatinous egg masses on the root surface (Plate 7 A-C). Symptoms may not be apparent on lightly infected root systems so that infected nursery stock mEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
ay easily go undetected. Feeder roots decay faster due to loss of integrity at the epidermis and at feeding sites in the cortex resulting in invasion Chapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 heavy infections result in cortical sloughing and root death.BiologyThe biology of T. semipenetrans is described in Chapter 1. The life cycle is regulated by host phenology in addition to seasonal changes in the soil environment. There may be one (Prasad & Chaw la, 1965; Bello ft al., 1986) or two ( Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 Vilardcbó, 1964; O'Bannon et al., 1972; Salem, 1980; Baghel &. Bhatti, 1982; Duncan & Noling. 1988d) distinct periods of active population developmentEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
per year, although no consistent seasonal periodicity in the number of eggs hatching per gram of root occurred during a survey in Israel (Cohn. 1966)Chapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 1972; Duncan &. Noling. 1987). This is often the period of maximum female fecundity. During the spring season (April-May), soil populations continue to increase and reach the highest annual level, even though fecundity may be lower than during the autumn (O'Bannon & Stokes, 1978; Duncan & Noling. 1 Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 9886). Lowest population levels occur during the summer and, depending on cumulative temperatures, during the winter. Thus, the autumn growth flush ofEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
roots may represent a major part of the food source for Florida populations of T. semipeneirans. Population growth slows or becomes negative as winteChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 for nematode development during the summer months. Population decline during this season may be partly due to factors such as increased biological antagonism, reduced availability of young feederNEMATODE PARASITES OF CITRUS323roots that may be most suitable for penetration and development (Cohn, 19 Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 64) or reduced availability of carbohydrates in roots during early fruit set and development. A model of T. semipenetrans seasonal populations dynamicEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
s was derived from data from a Florida survey (Duncan & Noling, 19886). The model predicts regular, seasonal population changes, the magnitude of whicChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 ability (Baines et al., 1969fl,6). Since the races vary somewhat by geographic region, so do suitably resistant cultivars. Within citrus, cultivars of Ponarus trifoliata arc resistant to most populations of T semipenetrans. Several hybrids of p. trifoliata and c. sinensis such as Troyer citrangc and Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 Carrizo citrange arc resistant to infection by some, but not all. populations of citrus nematodes (DuCharmc, 1948; Cohn. 19656 ; Feder, 1968; BainesEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
et al., 19696 )and there IS evidence from greenhouse trials that they may tolerate infection without significant damage (Kaplan & O’Bannon. 1981). ResChapter 9Nematode Parasites of CitrusLarry w. DUNCAN and Eli COHNUniversity of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Sta Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 future. Swingle citrumelo (C. paradisi X p. irifoliata )is a commercially acceptable rootstock with a high degree of resistance to all known populations of T. semipenetrans. Severinia buxtfolia is a citrus relative with a high degree of resistance to the citrus nematode which may become a source of Ebook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2 germplasm in intergencric breeding programs.Based on a number of reports, four biotypes of the nemtode were proposed (Inscrra et al., 1980; GottliebEbook Plant parasitic nematodes in subtropical and tropical agriculture: Part 2
et al., 1986). A “Citrus” biotype was described from populations found throughout the United States citrus-growing regions and Italy. It reproduces poGọi ngay
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