Contribution of sunflower plant breeding to Sclerotinia sclerotiorum head rot resistance in Argentina

Published on: 05/18/2007

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Author : CASTAÑO FERNANDO, Rodríguez Raúl, Ré José, Sequeira Claudio (INTA)

One of the objectives of sunflower plant breeders is to develop hybrids with a moderate resistance level to head rot caused by Sclerotinia sclerotiorum, one of the most important diseases affecting this crop. In this work we evaluated the impact that genetic improvement had on the resistance to this disease in hybrids grown in Argentina.

MATERIALS AND METHODS

Twenty-four hybrids, released in Argentina between the years 1973 and 2000 (YR), were evaluated in two environments, following a randomized complete block design with two replicates. Artificial S. sclerotiorum infections were made according to a current protocol.

Disease level was estimated at maturity for the following resistance components: incidence, incubation period, and severity.

Responses of sunflower hybrids, released in Argentina between 1973 and 2000, to S. sclerotiorum infections in two environments.

Hybrids	Environments Year of release	Balcarce		Camet		Incubation Index(&)
Hybrids	Environments Year of release	Incidence (%)	Severity (%)	Incidence (%)	Severity (%)	Incubation Index(&)
891	1973	100	96	100	95	0.69
G 97	1977	100	97	94	100	0.89
G 98	1980	100	100	76	100	0.93
G 90	1981	100	100	93	100	0.67
CONTIFLOR 3	1983	100	97	84	100	0.75
G 100	1984	100	98	100	99	0.78
G 103	1986	100	100	100	100	0.72
CONTIFLOR 9	1989	100	88	77	96	1.09
CONTIFLOR 15	1989	100	75	96	100	0.90
RANCUL	1991	100	98	98	100	0.78
ACA 884	1991	100	94	81	100	0.96
DEKASOL 3881	1993	100	100	93	100	0.78
DEKASOL 4030	1993	100	95	100	100	0.78
MORGAN 742	1995	100	93	77	100	1.00
DEKASOL 3900	1996	100	100	86	97	0.95
PARAISO 20	1996	100	95	53	76	1.08
DEKASOL 3915	1997	100	95	75	97	1.04
DEKASOL 4040	1997	100	100	98	100	0.67
MG 2	1998	100	95	87	100	0.82
MILENIO	1999	100	100	87	100	0.72
MG 4	1999	100	100	84	100	0.91
DEKASOL 4050	1999	100	99	88	91	0.90
CF 13	2000	100	94	75	98	0.92
Mean		100	96	87	98	0.85
LSD (p=0.05)			10	2	2	0.13
CV (%)			5	4	31	0.60

(&): across environments

RESULTS AND DISCUSSION

Combined analysis of variance detected highly significant effects of hybrids for all resistance components, and of environments and hybrid-environment interaction for incidence and severity. The correlation between YR and incubation period was significant and low (r = 0.24), as so as the regression of incubation period on YR (b = 0.005).

Hybrids did not show any variation of their disease level across YR for incidence and severity, but the first symptoms of the disease on modern hybrids appeared later than on the older ones, thus indicating there was a genetic gain for the incubation period for the hybrids released between 1973 and 2000. If this trend continues in the future, next hybrids could also show a lower incidence, which is the only component of head rot resistance being selected by most Argentinean sunflower breeders.

Authors: CASTAÑO FERNANDO¹, Rodríguez Raúl¹, Ré José², Sequeira Claudio².
¹ Unidad Integrada Balcarce (Facultad de Ciencias Agrarias-UNMdP/EEA-INTA), CC 276, B 7620 BKL Balcarce, Argentina.
² Monsanto Argentina SA, Camino Provincial 7, B 7612 Pueblo Camet, Argentina.