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This week, I will give my presentation in Japanese with English slides. The content will be two. One is on "Pistil Response to Temperature in Cherimoya (Annona cherimola Mill.),"on which I have been focused since 2009. The other is on "Effect of Artificial Medium Conditions and Storage Conditions on in vitro Pollen Germination and Pollen-tube Growth in Lychee (Litchi chinensis Sonn.) ," which has been examined in this year.
1. Pistil Response to Temperature in Cherimoya (Annona
cherimola Mill.)
Cherimoya is one of subtropical fruit trees native to
South America. Because of dichogamous flower, hand-pollination is
necessary in regions with no insect pollinators. Although
flowering occurs from spring to summer, it is empirically well
documented that the beginning and ending periods of flowering are
marked by remarkably unstable fruit set, which is troubling
problem for cherimoya growing in warm regions with large seasonal
differences in temperature, such as Japan. High or low
temperature is considered to be one of the main factors of low
fruit set. However, the response to temperature of reproductive
organs was still unknown.
Thus, by incubating pollinated flowers, we clarify the effect of
temperature on pollen-tube growth in pistils (Matsuda et al.,
2011). Then, to specify the critical periods for changes in
pistil receptivity, we chronologically observed pollen-tube
growth in pistils incubated after pollination throughout
flowering season. In addition, we examined the factors affecting
the receptivity (Matsuda and Higuchi, 2012).
Pollen tubes growth in pistils was fast at 20-27C,
suppressed below 15C, and inhibited over 30C.
The pistil receptivity for pollen tubes was low and many impaired
ovules were observed during early-mid spring, when the minimum
temperatures were approximately 10C. Although pollen-tube
growth was faster and ovule malformation decreased, a large
deviation in pistil receptivity was observed during late spring,
when the minimum temperatures were often over 15C. Pistil
receptivity was highest during early summer, when the
temperatures were 15-30C. After mid summer, when day/night
temperatures often exceeded 30/25C, pistil receptivity
remarkably decreased and many impaired ovules were observed.
Besides low viability of pollen, the difficulty in fruit set in
early spring and in summer was considered to be attributed to
impaired pistil development.
2. Effect of Artificial Medium Conditions and Storage Conditions
on in vitro Pollen Germination and Pollen-tube Growth in
Lychee (Litchi chinensis Sonn.)
Lychee is one of subtropical fruit trees native to
southern China. Flowering consists of three bloom; male (M1),
female, pseudohermaphrodite (functions as male, M2). M1 bloom has
little role in insect pollination because of its little amount of
nectar resulting in little visit of honey bees. If pollen
collected from M1 bloom could be stored until female bloom, or if
pollen collected from M2 bloom could be stored until the next
year female bloom, elongation of pollination period would be
expected, resulting in high fruit productivity or long-term
harvesting.
Thus, first, I determined optimal artificial medium condition for
in vitro pollen germination and pollen-tube growth. Then,
to effect of storage conditions, I tested in vitro viability of
pollen stored at -40, -10, 5, or 20C.
Optimal sugar concentration of artificial medium was 15%,
boric acid concentration was 10 ppm, and agar concentration was 1%.
Optimal temperature for pollen germination and pollen-tube growth
was 25C in 'Chakrapat' and 25-30C in 'Bengal.' Pollen
viability stored at 20C without siica gel decreased and lost
within after 6 weeks. Pollen stored at 20C with silica gel kept
as high viability as fresh one until after 6 weeks. At 20C,
pollen kept as high viability as fresh one until after 6 weeks
whether with silica gel or not. Pollen freezing at -40C and -10C
also showed as high viability as fresh one when storing for 30
days. Pollen Stored at -40C and -10C for 360 days will be
tested in 2013.
Thank you very much.
Hiroshi Matsuda