LIBRO-CONGRESO-CITRUS

S15
It produces orange-brown lesions on petals, inducing the abscission of young fruitlets and the retention of
the calyces. This study was undertaken to determine the effect of the following treatments (g or mL/hL):
T1- nontreated control, T2- quaternary ammonia (QA) 0.5; T3- QA 0.25; T4- famoxadone/mancozeb (FA MA)
(0.3125 31.25); T5- (FA MA) QA (0.3125 31.25) 0.5; T6- carbendazim (CA) 2.5; T7- CA QA 2.5 0.25; T8- CA
QA 2.5 0.5; T9- fenilpiridinilamina (FE) 0.0125; T10- FE QA 0.0125 0.5, T11- trifloxystrobin/tebuconazole (TR
TE) (0.2 0.4); T12- (0.2 0.4) 0.5; T13- conventional farm (CF) difenoconazole 0.3125 at first application plus
three additional applications of CA at 2.5; T14- CF QA 0.5. All treatments consisted of four applications of
fungicides at the appropriated flowering stages which were begun at pinhead stage. Intervals of applications
were 7-13 days. The assessments were made by measuring the amount of flowers with symptoms, effective
average number of fruits and number of fruit at harvest. The treatments T-11 and T-12 proved to be the
most effective, reducing the abscission of young fruitlets and increasing the retention of the bottom and,
consequently improving fruit set (P≤0.05). QA was effective only it was applied plus TR TE.
S15O09
Pathogenicity and genetic relationship of strains of Elsinoë australis causing Citrus Scab disease
Hyun J.W. 1 , Yi P.H. 1 , Yun S.H. 1 , Hwang R.Y. 1 , and Levy L. 2
1Citrus Research Station, National Institute of Horticultural & Herbal Science, RDA, Jeju, 697-943 (NIHHS, RDA), S. Korea; and 2National Plant Germplasm and Biotechnology Laboratory, USDA-APHIS-PPQ-CPHST, Beltsville, MD20705, USA. hyunjaewook@korea.kr
Two Scab diseases are recognized currently on citrus: Citrus Scab, caused by Elsinoë fawcettii, and Sweet
Orange Scab, caused by E. australis. Six pathotypes of E. fawcettii and two of E. australis have been described
to date based on host range. The pathogenicity and genetic relationships among 15 isolates of E. australis
from Korea, USA, Argentina and Brazil were investigated in this study. Based on pathogenicity tests on seven
differential hosts, all isolates did not induce any symptoms on leaves of the seven differential hosts. In assay
on fruit, the isolate Na-1 and KNa-2 induced the symptoms on natsudaidai but not on satsuma mandarin
fruits at all. The isolate Ea-2 induced symptoms on sweet orange fruit. By sequence analysis of Eaut-1, 2, 3,
4, EaNat-1 and 2 gene, the isolates were divided into three subgroups, natsudaidai pathotype group, south
American isolates group and USA isolates group, and the natsudaidai pathotype isolates and isolates from
USA were more closely related. We think that there is possibility that E. australis isolates were differentiated
to some pathotypes or genotypes in this study.
S15O10
Association and interaction of edaphic factors with root disease related citrus decline
Pretorius M.C. 1 , Labuschagne N. 2 , Kotze C. 1 , and McLeod A. 3
1Citrus Research International (CRI), Nelspruit, South Africa; 2University of Pretoria (UP), Pretoria, South Africa; and 3University of
Stellenbosch (US), Stellenbosch, South Africa. mc@cri.co.za
Symptoms associated with root disease related citrus decline include sparse foliage, twig die-back and reduced
growth, yield and fruit size as well as root rot. The causal factors involved in root disease related decline have
not yet been fully elucidated. Invariably tree decline is noticed too late for the implementation of preventative
management strategies. The aims of the study are to elucidate edaphic factors associated with citrus decline,
so that early-diagnostic tools can be developed. Two declining orchards were selected for the study. Based
on visual decline ratings of tree canopies, trees from three to four decline categories were selected. For
each tree category several parameters were measured including yield, soil and leaf characteristics, soilborne
pathogens and root disease associated symptoms. Multivariate analyses indicated that the two orchards were
distinct. Subsequent analyses were therefore conducted separately for the two orchards. Distinct groups
were identified for each tree category, indicating that most trees were visually correctly selected. Principal
component analyses of the four groups of data revealed that the strongest structure existed for yield data,
followed by soil factors, disease associated factors, and leaf parameters describing 81%, 61%, 49% and 39%
of the variability respectively. Continued multivariate analyses will allow identification of the progressive
changes in soil environmental interactions that lead to tree decline.
258 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012