LIBRO-CONGRESO-CITRUS

S15O06
Epidemiology of Alternaria Brown Spot of mandarins under semi-arid conditions in Spain
Bassimba D.D.M., Mira J.L., and Vicent A.
Instituto Valenciano de Investigaciones Agrarias (IVIA), Centro de Protección Vegetal y Biotecnología, Spain. dissolu15@hotmail.com
Alternaria Brown Spot (ABS) of mandarins, caused by Alternaria alternata, is a serious disease both in humid
and semi-arid citrus-growing regions. The pathogen affects leaves and fruit of susceptible cultivars such as
‘Fortune’, ‘Nova’, ‘Minneola’, and ‘Murcott’. The epidemiology of ABS was studied mainly in humid areas
in Florida but, due to climatic differences, this information cannot be extrapolated to semi-arid regions
like Spain. Fields studies were conducted in 2011 and 2012 in the experimental orchards at IVIA, Valencia.
Airborne dynamics of Alternaria conidia were monitored weekly by a spore trap, and the percentage of
pathogenic isolates was determined periodically using the selective medium ARSA and pathogenicity tests.
The presence of inoculum on affected leaves, shoots, leaf litter, and weeds was also determined. Infection
periods were monitored weekly by exposing trap plants of ‘Fortune’ and ‘Nova’, and environmental variables
were recorded by an automated meteorological station. Alternaria conidia were detected through the period
of study, but only 5% of the isolates were pathogenic. Although affected leaves and shoots were the main
source of inoculum, the survival of the fungus in the leaf litter was higher than previously reported in Florida.
Pathogenic isolates were detected also in weeds, but only at very low levels. Infections in trap plants occurred
mainly May-June and September-October. A significant positive correlation was detected between disease
incidence and rains. Funding: INIA RTA2010-00105-00-00-FEDER.
S15O07
Spray deposition benchmarks for control of Alternaria Brown Spot and evaluation of adjuvants
to improve fungicide spray deposition in citrus orchards
van Zyl J.G. 1 , Schutte G.C. 2 , and Fourie P.H. 1
1 Citrus Research International, Department of Plant Pathology, Stellenbosch University (CRI/USPP), South Africa; and 2 Citrus Research
International (CRI), South Africa. gideonvzyl@sun.ac.za
Lack of citrus fruit and foliar disease control is regularly attributed to poor fungicide spray deposition. A deposition
assessment protocol using fluorometry, photomacrography and digital image analysis was developed to study
improvement of spray application which proved to be very accurate in determining deposition parameters on
spray targets. To determine deposition benchmarks, young ‘Nova’ mandarin leaves were sprayed with copper
oxychloride and SARDI Yellow Fluorescent Pigment at different concentrations and spray deposition assessed.
Leaves were spray inoculated with Alternaria alternata [Alternaria Brown Spot (ABS) of mandarins] and symptoms
rated. A strong linear relation was found between treatment concentration, leaf area covered by fluorescent
pigment particles (%FPC) and Cu residue analysis. ABS control was modelled on %FPC and benchmarks for
50% and 75% control were calculated. Selected adjuvants were evaluated in laboratory spray- and biological
efficacy trials. Treatments varied significantly in deposition quantity and ABS control, but these parameters
were poorly correlated, also with control levels predicted from the %FPC benchmark model. Deposition quantity
and Cu-residues could only partially explain the level of control achieved following the addition of adjuvants.
These anomalous results could be attributed to the effects of adjuvants on deposition quality, on pathogen
development and synergistic effects between adjuvant and fungicide.
S15O08
Chemical control of Colletotrichum acutatum and C. gloeosporioides, causal agents of Citrus
Postbloom Fruit Drop in Brazil
Goes A. 1 , and Rinaldo D. 2
1 Universidade Estadual Paulista (UNESP), Phytopathology, Brazil; and 2 Universidade Estadual Paulista (UNESP), Phytopathology, Brazil.
adggoes@yahoo.com.br
Postbloom Fruit Drop (PFD) in Brazil is caused by Colletotrichum acutatum and C. gloeosporioides. PFD is
one of the most important fungal diseases of sweet orange in tropical and subtropical regions of the world.
XII INTERNATIONAL CITRUS CONGRESS 2012 - 257
S15