Evaluating methyl jasmonate for induction of resistance to Fusarium oxysporum, F. circinatum and Ophiostoma novo-ulmi

Abstract

Damping off is probably the most common disease affecting seedlings in forest nurseries. In south-western Europe, the pitch canker and the Dutch elm disease cause relevant economic looses in forests, mostly in adult trees. The ability of the chemical plant elicitor methyl jasmonate (MeJA) to induce resistance in Pinus pinaster against Fusarium oxysporum and F. circinatum, and in Ulmus minor against Ophiostoma novo-ulmi was examined. In a first experiment, an aqueous solution of MeJA 5 mM was applied to P. pinaster seeds by immersion or spray, and different concentrations of MeJA (0, 0.1, 0.5, 1, 5 and 10 mM) were tested in seedlings before inoculations with F. oxysporum (10 5 and 10 7 spores mL -1 ). In a second experiment, 6-months-old P. pinaster seedlings were sprayed with 0 and 25 mM of MeJA, and later challenged with mycelium of F. circinatum. Finally, 4-year-old U. minor trees were sprayed with 0, 50 and 100 mM of MeJA and subsequently inoculated with O. novo-ulmi (10 6 spores mL -1 ). MeJA did not protect P. pinaster seeds and seedlings against F. oxysporum, probably because plants were too young for the physiological mechanisms responsible for resistance to be induced. Based on the morphological changes observed in the treated 6-months-old P. pinaster seedlings (reduction of growth and increased resin duct density), there is evidence that MeJA could have activated the mechanisms of resistance. However, 25 mM MeJA did not reduce plant mortality, probably because the spread of the virulent F. circinatum strain within the tree tissues was faster than the formation of effective defense responses. Based on the lack of phenological changes observed in the treated elms, there is no evidence that MeJA would cause induction of resistance. These results suggest that the use of MeJA to prevent F. oxysporum and F. circinatum in P. pinaster seedlings in nurseries and O. novo-ulmi in U. minor trees should be discarded.

Strong in vitro antagonism by elm xylem endophytes is not accompanied by temporally stable in planta protection against a vascular pathogen under field conditions

“…Other environmental factors, such as the chemical environment (Martín et al 2008b(Martín et al , 2010aVivas et al 2012) or the action of less aggressive Ophiostoma strains inducing tree resistance (Hubbes and Jeng 1981;Jeng et al 1983) should not be discarded as factors involved in environmental resistance. A deeper study of the fungal microbiome and its spatial distribution over the tree architecture, including seeds, could help to identify candidate mutualistic endophytes in elms.…”

Seven Ulmus minor clones tolerant to Ophiostoma novo-ulmi registered as forest reproductive material in Spain

“…From the experience of the Spanish elm breeding programme, the high level of polymorphism obtained with the microsatellites selected allows rigorous identification of each clone. 196 196 196 196 194 196 194 198 196 196 196 196 194 194 The Spanish programme aimed to directly control DED (Solla & Gil 2003, Martín et al 2010b, Vivas et al 2012) and gain a better understanding of tolerance through new techniques (Martín et al 2005(Martín et al , 2007(Martín et al , 2008a. One of its medium-term priorities is to increase the genetic diversity of tolerant native elms.…”

Environmental Maternal Effects Mediate the Resistance of Maritime Pine to Biotic Stress

“…This invasive forest pathogen is native to North America but has been recorded in various countries outside its natural range [25] and has greatly impacted most Pinus plantations worldwide [26]. In Spain, it was first isolated in nurseries and forest plantations of P. radiata and P. pinaster [27] and is now apparently well established in the north, representing the main threat to Pinus in this area [28], [29]. It has recently been shown that genetic selection of P. pinaster genotypes less susceptible to the pathogen could be an adequate measure to reduce the impact of the disease [30].…”