Pineapple Sweet Orange Research Articles

Host range and symptomatology of a graft-transmissible pathogen causing bud union crease of citrus on trifoliate rootstocks

A graft-transmissible pathogen causing bud union crease of Nagami kumquat SRA–153 on Troyer citrange was characterized for host range and symptomatology. Buds of Marsh grapefruit, Nules clementine, Eureka lemon and Pineapple sweet orange preinoculated with kumquat SRA–153 were propagated on citrange rootstocks. Some plants of Nules clementine and Eureka lemon had developed bud union crease six months after propagation, whereas all Marsh grapefruit and Pineapple sweet orange plants still showed normal bud union after one year. On indexing these preinoculated species, Nules clementine and Eureka lemon caused vein clearing in Pineapple sweet orange and Dweet tangor, chlorotic blotching in Dweet tangor and stem pitting in Etrog citron, whereas Marsh grapefruit and Pineapple sweet orange caused only chlorotic blotching in Dweet tangor and stem pitting in Etrog citron. Following shoot-tip grafting in vitro of kumquat SRA–153, kumquats 38–1 and 497–2 obtained from it caused chlorotic blotching in Dweet tangor and stem pitting in Etrog citron, but not vein clearing in Pineapple sweet orange and Dweet tangor or bud union crease when propagated on citrange. These results suggest the presence of at least two pathogens or pathogen strains in kumquat SRA–153 and the elimination of one of them after shoot-tip grafting in vitro or inoculation on Marsh grapefruit or Pineapple sweet orange. They also indicate that the pathogens in kumquat SRA–153 can be detected by indexing on Dweet tangor or Etrog citron.

Effects of Host Plant and Temperature on the Biology ofToxoptera citricida(Homoptera: Aphididae)

Development reproduction, and population growth parameters of the brown citrus aphid. Toxoptera citricida (Kirkaldy), were evaluated at 25 degrees C on 5 citrus-related host plants ('Carizo','sour orange'. 'Duncan grapefruit', 'Pineapple sweet orange', and 'Mexican lime'), and at 3 temperatures (20, 25, and 30 degrees C ) on 'sour orange'. Brown citrus aphids had faster nymphal developmental times on 'Carrizo' and 'sweet orange' (6.7 d) compared with the other host plants (7.5-7.6 d). Aphids reared on 'Carrizo' had the highest fecundity (67.5 offspring/aphid) and daily reproduction (3.8 offspring/aphid/d). The net reproductive rate (62.6 offspring/aphid/generation) on 'Carrizo' was 21%, 49%, 53%, and 77% higher and the population doubling time (1.8 d) was 2%, 13%, 14%, and 20% faster compared with on 'sweet orange', 'sour orange', grapefruit, and 'Mexican lime', respectively. Development of nymphs was completed in either 4 or 5 instars. The brown citrus aphid had longer nymphal developmental times and adult reproductive periods at 20 degrees C (9.0 and 22.2 d, respectively) compared with at 25 degrees C (7.5 and 15.2 d) and 30 degrees C (6.3 and 11.2 d). The moderate temperature (25 degrees C) was optimal for the brown citrus aphid population growth and intrinsic rate of increase (0.33) was highest. Fecundity of brown citrus aphids reared at 30 degrees C in Florida (our data) was approximately equal to 10 times greater, and r(m) was twice as large as those reared under similar conditions in Japan (data from Komazaki 1982). It was concluded that brown citrus aphid populations in Florida could tolerate higher temperatures than the populations in Japan, and that different populations of brown citrus aphids may have greater genetic variation than was previously thought.

Root Regeneration and Tolerance of Citrus Rootstocks to Root Rot Caused byPhytophthora nicotianae

Graham, J . H. 1995. Root regeneration and tolerance of citrus rootstocks to root rot caused by Phy1opl11hora nicotianae. Phytopathology 85: 111117. Citrus rootstock cultivars varying in tolerance to fibrous root rot were evaluated for their ability to regenerate roots in the presence of potentially damaging populations of Phytophthora nicotianae. In chlamydospore­ infested soils in the greenhouse, tolerance to root rot generally was exhibited as more rapid growth of undisturbed and pruned roots of the rootstocks trifoliate orange and Swingle citrumelo compared with Carrizo citrange, sour orange, Ridge Pineapple sweet orange, and Cleopatra man­ darin. The capacity for regeneration of Volkamer lemon roots in the presence of P. nicotianae varied with experiments and was associated with differences in greenhouse temperature conditions. In a field trial with damaging populations of P. nicotianae, growth rates of regenerating Phytophthora nicotianae Breda de Haan (syn. P. parasitica Dastur.) infects the root cortex and causes a decay of fibrous roots of all commercial citrus rootstocks in Florida (2, I0 , 11). Root rot can be especially severe in infested soils of citrus nurseries (2 1). In orchards, damage of fibrous roots causes tree decljne and yield losses (14,15, 17). With mature trees, the production of new fibrous roots apparently does not keep pace with root death, and the tree is unable to maintain adequate water and mineral uptake to sustain maximum fruit production (14). Rootstocks are referred to as tolerant rather than resistant because fibrous roots become infected under artificial inoculations (5,6,10) and in infested nursery and orchard soils (2). Tolerance was previously defined as the condition in which plants are infected but show little or no net root loss either because infected roots do not rot or because root mass density is maintained by root regeneration ( 10). Recent greenhouse evaluations with chlamydo­ spore inoculum in soil revealed that most commercial rootstocks in Florida were intolerant to root rot caused by P. nicotianae ( 10). In contrast, trifoliate orange (Poncirus trifoliata (L.) Raf.) and its hybrid, Swingle citrumelo (Citrus paradisi Macf. X P. trifoliata), were considered tolerant. Volkamer lemon (C. volkameriana Pasq.) was judged as intermediate in tolerance. In greenhouse inoculations, tolerance of trifoliate orange and Swingle citrurnelo appeared to be related to the capabiUty of these rootstocks to regenerate roots in the presence of P. nicotianae (10). In Florida rootstock trials, trifoliate orange and Swingle citru­ melo supported lower soil populations of P. nicotianae, whereas intolerant rootstocks had higher population densities in the soil of the root zone (2), here defined as rhizosphere populations.

Temporal and Spatial Dynamics of Postbloom Fruit Drop of Citrus in Florida

Temporal progress of postbloom fruit drop of citrus in Florida was studied in four experimental plots of 25-81 3- to 4-yr-old trees of Valencia sweet orange in Gainesville and Lake Alfred and of Pineapple sweet orange and Ruby Red grapefruit in Hastings. Blossoms of central focal trees in each plot were inoculated with the slow-growing orange strain of Colletotrichum gloeosporioides. Incidence of trees and of open blossoms with postbloom fruit drop was monitored over time. Directionality of spread from a point source was measured in four contiguous quadrants of each plot. Disease gradients were estimated on four transects radiating from a central focal tree. Disease increased in intensity and spread in space following rain events in all four plots [...]

Growth and Morphogenesis of Citrus Tissue Cultures Infected with Psorosis, Vein Enation, and Cachexia

Stem segments from Pineapple sweet orange (Citrus sinensis) and Etrog citron (C. medica) infected with psorosis, vein enation, and cachexia, as well as uninfected controls, were cultured in vitro. Production of roots and regeneration of shoots and buds were modified as a result of infection. The number of explants showing morphogenesis and the amount of rooting and/or regeneration of shoots and buds were affected as compared with the uninfected explants cultured as controls. The differences on morphogenic patterns depended on the disease and the disease isolate (...)

Evaluation of Tolerance of Citrus Rootstocks to Phytophthora Root Rot in Chlamydospore-Infested Soil

Seven citrus rootstocks of commercial importance in Florida were evaluated for their tolerance to Phytophthora root rot. Six-month-old seedlings were planted in soil artificially infested with chlamydospores at 0, 0.5, 1, 5, and 10 propagules of Phytophthora parasitica per cm 3 of soil. For all rootstocks, at 6 wk after inoculation there was little increase in disease rating with an increase in inoculum density above 1 propagule/cm 3 . Disease severity at the higher inoculum densities was significantly greater for the susceptible rootstocks (sour orange, Ridge Pineapple sweet orange, Cleopatra mandarin, and Carizzo citrange) than for the tolerant rootstocks (trifoliate orange and Swingle citrumelo) (...)

Influence of virus and virus-like agents on the development of citrus buds cultured in vitro

Tissue culture in vitro was used to determine the effect of six major citrus virus and virus-like agents. Nodal stem segments from inoculated Pineapple sweet orange (Citrus sinensis (L.) Osb.), Mexican lime (C. aurantifolia (Christm.) Swing.) and Arizona Etrog citron 861-Sl (C. medica L.) were cultured in vitro to induce shoots. Some virus and virus-like agents had a marked effect on bud development and further recovery of plantlets. The number and size of the shoots that developed from each bud were affected as a result of infection. The effect depended on the specific virus, the isolate and the host-disease combination. The possible implications of these results are discussed.

Salinity and flooding stress effects on mycorrhizal and non-mycorrhizal citrus rootstock seedlings

Seedlings of the rootstocks Pineapple sweet orange (SwO), Carrizo citrange (CC), and sour orange (SO) were grown in low phosphorus (P) sandy soil and either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus intraradices, or were non-mycorrhizal (NM) and fertilized with P. VAM and NM seedings of similar shoot size and adequate P-status were selected for study of salinity and flooding stress. One-third of each of the VAM and NM plants were given 150 mM NaCl for a period of 24 days. One-third of the plants were placed into plastic bags and flooded for 21 days while the remaining third were non-stressed controls. In general, neither stress treatment affected mycorrhizal colonization. Salinity stress reduced the hydraulic conductivity of roots, leaf water potential, stomatal conductance and net assimilation of CO2 (ACO2) of mycorrhizal and non-mycorrhizal seedlings to a similar extent. VAM plants of CC and SO accumulated more Cl in leaves than NM plants. Cl was higher in non-mycorrhizal roots of SwO and CC than in mycorrhizal roots. Flooding the root zone for 3 weeks did not produce visible symptoms in the shoot but did influence plant water relations and reduce ACO2 of all 3 rootstocks. VAM and NM plants of each rootstock were affected similarly by flooding. Comparable reduction in nitrogen and P content of both mycorrhizal and non-mycorrhizal plants suggested that flooding stress was primarily affecting root rather than hyphal nutrient uptake.

Experimental Transmission of Citrus Blight

eight healthy 6-yr-old Pineapple sweet Tucker, D. P. H., Lee, R. F., Timmer, L. W., Albrigo, L. G., and Brlansky, R. H. 1984. orange trees on rough lemon rootstock Experimental transmission of citrus blight. Plant Disease 68:979-980. from a grove in Lake Alfred unaffected by blight were pruned and transplanted Eight mature, blight-affected Pineapple sweet orange (Citrus sinensis) trees on rough lemon (C. as described. These receptor trees were jambhiri) rootstock were transplanted to an area of low blight incidence. Healthy trees of bearing planted adjacent to the donor trees with age and of the same cultivar were transplanted next to each blight-affected donor tree and several roots each of the healthy, receptor trees and the blighted donors were splice-grafted together. An the trunks about 1.2 m from those of the equal number of control trees was transplanted to an adjacent row. After 3 yr, receptor trees had donors. Five to 10 roots about 1-2 cm in significantly higher concentrations of zinc in trunk phloem than the controls. After 4 yr, seven of diameter from each receptor tree were eight receptor trees had typical visual symptoms of blight, significantly higher concentrations of splice-grafted to similar roots on the zinc in trunk wood, lower water uptake, and amorphous plugs in the vessels of the trunk. Only one corresponding donor tree. Eight additional of eight control trees developed these typical blight symptoms. This is the first report of healthy 6-yr-old Pineapple sweet orange experimental transmission of citrus blight. trees on rough lemon were transplanted similarly from the same grove as the receptor trees to an adjacent row 4.5 m Citrus blight is a vascular wilt disease trees under field conditions. Lima and from the blight-affected donors as of unknown cause. Losses from the Borducchi (6) also graft-transmitted a ungrafted controls for the root-grafted disease have been severe, reaching 'zinc accumulation to young trees receptors. 500,000 trees per year in Florida, with from blight-affected sources, but these At various times during the experiment, loss rates in individual groves as high as trees did not show decline symptoms. several diagnostic techniques were used 10-20% per year (11). Progress in blight Transmission of a zinc accumulation to evaluate the status of the donor, research has been slow because blight factor was not confirmed in other studies receptor, and control trees. Canopy does not develop in trees less than 5-8 yr (13). In all previous work, no one has symptoms were rated on a scale of 0 = old and the disease has not been induced artificially induced a tree to decline from healthy, 1 = mild (leaves small with experimentally (10). In early work, blight or reproduced all of the known symptoms of zinc deficiency, internodes Rhoads (7) concluded that blight was a symptoms of the disease in a mature tree. short, slight wilt but little or no thinning nonparasitic disorder after failure to It has been generally agreed that the of foliage), 2 = moderate (leaves small, graft-transmit or propagate the disease. malady was nontransmissible (10). often flaccid, with symptoms of zinc Even after blight was more thoroughly Most studies have concentrated on deficiency, canopy sparse with some twig characterized and diagnostic tests transmission of blight symptoms to became available, bud propagations and young seedlings or propagation of the reconstitutions of blighted trees from disease by reconstituting new trees from Table 1. Diagnostic characteristics of the sprouted roots and buds of affected trees roots and buds of blight-affected trees. In blight-affected donor trees during the failed to reproduce the disease (9,13). this paper, we present the first evidence experiment. Feldman and Hanks (3) reported reduction that blight can be transmitted experiof root growth in rough lemon seedlings mentally and that all the characteristics of Characteristic Date Valuea

Accumulation and Metabolism of Bromacil in Pineapple Sweet Orange (Citrus sinensis) and Cleopatra Mandarin (Citrus reticulata)

Young orange [Citrus sinensis (L.) Osbeck ‘Pineapple sweet orange’] trees are more sensitive to bromacil (5-bromo-3-sec-butyl-6-methyluracil) than young mandarin (Citrus reticulata Blanco ‘Cleopatra mandarin’) trees. Pineapple sweet orange roots absorbed twice as much 14C from bromacil, and accumulated three times as much in the leaves, as did Cleopatra mandarin. The amount of conjugated metabolites formed was the same in the roots of the two cultivars, but twice as much formed in the leaves of Cleopatra mandarin as in the leaves of Pineapple sweet orange. The principle metabolite was 5-bromo-3-sec-butyl-6-hydroxymethyluracil; a minor metabolite was tentatively identified as 5-bromo-3-(3-hydroxyl-1-methylpropyl)-6-methyluracil. No 5-bromouracil was detected. Citrus cultivars differ in their ability to accumulate and metabolize bromacil into conjugated nonphytotoxic compounds.