Fernando Haddad

Identification of passion fruit genotypes resistant to Fusarium oxysporum f. sp. passiflorae

This study aimed to characterize the resistance of 31 passion fruit (Passiflora sp.) genotypes to Fusarium oxysporum f. sp. passiflorae (FOP). About 20 seedlings of each genotype were inoculated by immersing the roots in a suspension of 106 macroconidia mL-1 for five minutes and then transplanting them into pots containing a mixture of soil and sterile substrate. They were evaluated daily for 120 days for the occurrence of wilt symptoms and death. These data were used to calculate the area under the disease progress curve, for survival analysis and grouping. The mortality rate ranged from 0 to 100% and the AUDPC ranged from 0 for genotypes without symptoms of the disease to 6,650.63 for the hybrid HFOP-01. Genotypes were classified into four subgroups: resistant, moderately resistant, susceptible and highly susceptible. The resistance was genotype dependent, but no significant variation was found between the purple and the yellow P. edulis.

Molecular fingerprinting of Fusarium oxysporum f. sp. passiflorae isolates using AFLP markers

Fusarium oxysporum f. sp. passiflorae W.L. Gordon (FOP) is one of the most important fungal pathogens of passion fruits. Understanding molecular variation of isolates from different areas is of utmost importance. Molecular fingerprinting on 14 isolates of FOP were conducted using AFLP molecular markers (Amplified Fragment Length Polymorphism), and their genetic variability were estimated. Twenty-five AFLP primer combinations were selected for amplification of FOP isolates and one for Fusarium oxysporum f. sp. cubense W.C. Snyder & H.N. Hansen (FOC), resulting in 99% polymorphic fragments, with an average of 40 fragments per primer combination. Specific fingerprints could be generated for most of the isolates evaluated; we observed a high power of discrimination of the AFLP primer combinations, with the presence/absence of up to 26 specific fragments per isolate. Thus, specific fingerprinting was obtained for 10 of the 15 isolates analyzed. The values of the polymorphic information content, the index and the resolving power of the markers showed wide variation and reflected the high informative contents of the primers used in the characterization of the FOP isolates. The FOP isolates were divided into four groups, irrespective of their geographic origins, with the allocation of 5, 7, 1 and 1 FOP isolates into Groups II, III, IV and V, respectively. A wide genetic diversity was observed in FOP isolates, which should be taken into consideration when implementing strategies for the improvement of passion fruit in the search for cultivars with multiple resistance to different isolates.

Resistance to Fusarium dry root rot disease in cassava accessions

The objective of this work was to identify sources of resistance to dry root rot induced by Fusarium sp. in cassava accessions. A macroconidial suspension (20 µL) of 11 Fusarium sp. isolates was inoculated in cassava roots, from 353 acessions plus seven commercial varieties. Ten days after inoculation, the total area colonized by the pathogen on the root pulp was evaluated by digital image analysis. Cluster analysis revealed the presence of five groups regarding resistance. The root lesion areas ranged from 18.28 to 1,096.07 mm2 for the accessions BGM 1518 and BGM 556, respectively. The genotypes BGM 1042, BGM 1552, BGM 1586, BGM 1598, and BGM 1692 present the best agronomical traits.

SOURCES OF RESISTANCE TO Fusarium oxysporum f. sp.cubense IN BANANA GERMPLASM

Fusarium wilt (syn= Panama disease), caused by Fusarium oxysporum f. sp. cubense (FOC), is one of the most destructive diseases of banana, being genetic resistance the main management strategy for this disease. Since the pathogen is constantly evolving to supplant the genetic resistance, new sources of resistance must be investigated by genetic improvement programs aiming to developing new varieties. The objective of the present study was to identify sources of resistance from the different accessions maintained in the banana active germplasm bank (BAGB) at Embrapa Mandioca e Fruticultura. Forty-one BAGB accessions were evaluated, including 17 diploids, 21 triploids, and two tetraploids. The area under the disease progress curve, disease index, and incubation period were also evaluated. In relation to FOC resistance, there is genetic variability available among the BAGB accessions. The genotype M53 is notable for the complete resistance it expressed, and the accessions Birmanie, PA Songkla, Pirua, Imperial, Poyo, Ambei, Walebo, and Kongo FRF 1286 expressed quantitative resistance.