PCC MarchApril Final Draft

Figure 4. Susceptibility of various fig cultivars to limb dieback
pathogen Neoscytalidium dimidiatum.
Dr. Themis Michailides sampling symptomatic fig trees.
Continued from Page 26
Figure 5. Effect of stress factors (mallet wounding and sunburn)
and treatment with white wash affecting the severity of limb
dieback of fig.
Limb and branch samples from the majority of these orchards
had 60% to 100% Neoscytalidium, while three had 7% to 11%,
and two 26% to 32%. In 12 of these orchards, a second pathogen,
Phomopsis spp., was isolated along with Neoscytalidium in the
first year of the survey. Phomopsis sinarencis has been reported in
California causing an epidemic on Kadota figs back in 1935 and in
other countries as an important fig canker pathogen. By the third
year of this survey, less Phomopsis was isolated, and, very recently,
almost none was isolated, probably because the very susceptible
Kadota variety is rarely now planted in California. Phomopsis is
known as a pathogen fungus associated with canker diseases in
many other crops around the world, but more investigations are
needed to figure out its role in fig limb dieback.
Differences in Susceptibility
To determine if there were any differences in susceptibility to the
limb dieback pathogen, we inoculated six cultivars directly in the
field. We found that three months after inoculations, the cultivars
Kadota, Black Mission and Sierra developed twice as long canker
size than the cultivars Brown Turkey, Calimyrna and Conadria (Figure
4). Growers also reported that they see the problem to be more
severe in Black Mission than other cultivars. Inoculations of six cultivars
showed that Neoscytalidium is a plant pathogen that likes high
temperatures. For instance, it cannot grow below 50 degrees F; its optimum
temperature for growth is 90 to 95 degrees F, and it can even
grow at 104 degrees F to some extent. Therefore, this fungus likes hot
summer temperatures and prefers to infect sunburned branches and
pruning wounds.
Figure 6. Effect of Surround® spray on the severity of limb
dieback of fig.
In experiments, we inoculated shoots of fig of different ages, including
current growth (green) shoots, one-year, two-year and threeyear-old
shoots, by wounding and inoculating with either a mycelial
plug or a spore suspension. Interestingly, the three-year-old shoots
28 Progressive Crop Consultant March / April 2021