Variation in Resistance of Populus nigra to Sphaerulina musiva in the North-Central United States

Abstract

Populus nigra, commonly used in hybrid poplar breeding programs in the north-central United States, is susceptible to Septoria stem canker, caused by Sphaerulina musiva. In this study, two experiments were conducted to (i) characterize the variation in resistance of 47 genotypes of P. nigra collected from seven locations in Europe in terms of cankers per centimeter and disease severity score; (ii) determine whether location, isolate, genotype, or their interactions significantly affect cankers per centimeter and disease severity score; and (iii) examine the correlation of disease severity score between single-isolate and bulk-isolate inoculations. The majority of the variation in resistance for cankers per centimeter was explained by location (72%; P < 0.001) followed by genotype(location) (28%; P < 0.001). In contrast, the majority of the variation in disease severity score was explained by genotype–location (51%; P < 0.001) followed by location (26%; P = 0.025). The disease severity score model also indicated the presence of a significant isolate effect (P = 0.034) and genotype(location) × isolate interaction (P = 0.004). The correlation coefficients for disease severity score indicated a significant range of correlations (r = 0.871 to r = 0.952) when correlating single-isolate to bulk-isolate inoculations.

Growth parameters and resistance to Sphaerulina musiva-induced canker are more important than wood density for increasing genetic gain from selection of Populus spp. hybrids for northern climates

“…In a similar manner to the growth traits, canker resistance was not directly related to any particular hybrid type, which is often a subject of discussion in the literature (Dunnell et al 2016;Dunnell and LeBoldus 2017;Feau et al 2010;LeBoldus et al 2009;Lo et al 1995). In this case, our results are in line with previous findings by Ward and Ostry (2005) and LeBoldus et al (2009).…”

“…Our study also showed that canker infections negatively affected height growth and were associated with an increase in mortality among clones. These findings correspond to previous research, showing that canker is a significant factor influencing productivity and survival of hybrid poplar clones in managed plantations in North America (Dunnell et al 2016;Lo et al 1995). According to Lo et al (1995), annual biomass losses due to Sphaerulina musiva infection can be as high as 63% of the total yield, while the mortality of highly susceptible clones affected by cankers can reach 100% within 5-10 years after the establishment of the plantation (Mottet et al 2007).…”

“…Several studies carried out in controlled environment conditions have revealed, however, that the poplar clone genotype has a stronger impact on disease severity than the Sphaerulina musiva genotype itself and other abiotic factors (LeBoldus et al 2007;LeBoldus et al 2009). In addition, controlled inoculation experiments have shown that pathogen isolates and clone × isolate interaction effects were found to be lower than poplar clone genotype effects (Dunnell et al 2016;LeBoldus et al 2008) which suggests that Populus spp. clones should be subject to resistance screening under both controlled greenhouse conditions (LeBoldus et al 2009) in addition to field testing.…”

“…The only way to prevent the spread of Sphaerulina musiva is to plant resistant hybrid poplars. The results of controlled inoculation experiments have indicated that poplar genotype is a prominent factor in disease development and resistance to Sphaerulina musiva (Dunnell et al 2016;LeBoldus et al 2007;LeBoldus et al 2008;Qin and LeBoldus 2014), which implies a possible increase in resistance by appropriate selection of clones.…”

Vectors of Efficiency in Hybrid Poplar Genotype Testing

“…This fact is one of the strongest justifications for continuing poplar breeding programs. Recent papers on Sphaerulina musiva in hybrid poplars provide background on canker resistance research (Dunnell et al, 2016;Niemczyk and Thomas, 2020;Tabima et al, 2020), including the importance of deploying resistant clones.…”