LIBRO-CONGRESO-CITRUS

S15
Almost all of the high-fruit-quality parents developed so far by our breeding program are susceptible to this
disease necessitating the screening of their progeny. This is done by simply spraying 3-6 month old hybrid
seedlings with a spore suspension derived from a toxin-producing field isolate, then incubating these seedlings
in a cool room at 25°C and high humidity for five days. Susceptible seedlings show clear disease symptoms and
are culled. After using this approach for only two seasons we now have more than 11,000 hybrids growing in
field progeny blocks that are known to be genetically resistant to brown spot disease.
S15P13
Difference in susceptibility to Alternaria Brown Spot between young and mature ‘Minneola’
tangelo leaves
Liarzi O., Sela N., and Ezra D.
A.R.O., The Volcani Center, Bet Dagan, Department of Plant Pathology and weed research, Israel. dezra@volcani.agri.gov.il
Alternaria alternata, the cause of Alternaria Brown Spot, is an important disease of mandarins in Israel. This
fungus causes symptoms on fruit, shoots and young leaves of susceptible cultivars. A specific toxin (ACT),
produced by the fungus is well characterized but its specific target site in the host is still unknown. The fact
that symptoms are visible only on young leaves, suggest that there may be a factor(s) differentially expressed
in the young leaves, and absent from mature ones. Using the Suppression Subtractive Hybridization (SSH)
method we compared and isolated cDNA molecules expressed only in young (96 sequences) or mature (110
sequences) leaves. All sequences were analyzed using Blast2GO software. Gene ontology of the sequences
revealed differences between young and mature leaves. In order to find if these differences play a role in
gaining susceptibility or resistance to A. alternata of young and mature leaves, respectively, qPCR analysis of
selected genes in the presence and absence of the pathogen is in progress.
S15P14
Screening for Alternaria Brown Spot resistance in the triploid mandarin breeding programme in Spain
Bassimba D.D.M., Vicent A., Cuenca J., Aleza P., and Navarro L.
Instituto Valenciano de Investigaciones Agrarias (IVIA), Centro de Protección Vegetal y Biotecnología, Spain. dissolu15@hotmail.com
About 1,200-2,000 seedless hybrids are obtained each year in the triploid mandarin breeding program in Spain.
Some of the parents used, such as ‘Fortune’, ‘Murcott’ and ‘Minneola’, are susceptible to Alternaria Brown Spot
(ABS) caused by Alternaria alternata. The susceptibility to ABS is partially transmitted to the progeny, so evaluation
of genotype susceptibility was a critical target since the beginning of the breeding program. Traditionally, longterm
field trials under endemic disease conditions were used to evaluate disease susceptibility. However, these
experiments are costly, time-consuming, and difficult to apply with large numbers of genotypes. Therefore, two
alternative methodologies were evaluated. Detached young leaves in humid chambers and potted plants with
young shoots were inoculated by spraying a spore suspension. Different combinations of genotype, leaf age, spore
concentration, temperature, and leaf wetness duration were evaluated and used as explanatory variables. The
duration of the incubation period (i.e. from inoculation to symptom expression) and disease severity were used
as response variables. The inoculation of detached leaves discriminated only between susceptible and resistant
cultivars. The interaction between leaf age and incubation period duration in inoculated potted plants was
correlated with the degree of susceptibility observed in the field. The implementation of these two methodologies
facilitated the commercial release of new seedless triploid hybrids, such as ‘Garbí’ and ‘Safor’, resistant to ABS
despite that ‘Fortune’ is one of the parents. Funding: INIA RTA2010-00105-00-00-FEDER.
S15P15
Enhancing of physiological parameters improves resistance against Alternaria Brown Spot of mandarins
Llorens E., Fernández-Crespo E., Camañes G., Lapeña L., and García-Agustín P.
Universitat Jaume I (UJI), Departamento de Ciencias Agrarias y del Medio Natural. ESTC, Spain. ellorens@uji.es
The appearance of Alternaria Brown Spot (ABS) in Spanish citrus regions forced the abandonment of the
‘Fortune’ mandarin production due to the difficulty of controlling this disease with fungicides. Environmental
264 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012