Chapter 4 The Influences of Temperature and Seasonal Changes on Cytoplasm Male
4.4 Discussion
39
Peterson (1958) indicated that the floral organ of CMS pepper was similar to that of fertile pepper, but its stamens were approximate one-half of the size of fertile anthers and just produced few viable pollen grains occasionally. The color and size of anthers between CMS line while plants expressed male sterility and their maintainers was distinctly different. When unstable CMS hot pepper line ‘CCA 7243’ restored fertility, the phenotype of anthers in unstable CMS plants was as same as it in maintainer ‘PBC 385’ (Fig. 4.2 B and C), but sometimes no pollen grains were obtained in anthers of unstable CMS line and the fertility restoration needed investigate by light microscope.
The unstable CMS sweet pepper lines of AVRDC – The World Vegetable Center were recorded to restore their fertility approximately after 17 d incubated in 23/20oC growth chamber (unreported). Hong (2003) reported that the temperature at 20 d before anthesis could cause CMS hot pepper fertility restoration. According to the greenhouse and the field observations in this study, the process of pepper floral bud development stages from the visual bud to anthesis needed in almost 30 d, we suggested that the temperature at 30 d before unstable CMS plants showed fertility was related to plant fertility restoration.
Previous reports did not show the critical range of temperature that caused unstable CMS lines restore fertility. Shifriss (1997) suggested that CMS pepper lines restored
40
fertility when the temperature dropped below the optimal for pepper production (day/night temperature was 25/17oC). The other unstable CMS hot pepper line ‘AAC.
17’ could restore fertility at 25/18oC, 20/18 oC, and 20/12 oC growth chamber (Hong, 2003). The unstable CMS sweet pepper lines of AVRDC restored fertility when minimum temperature less than 18 oC in the field, and also restored at 23/20 oC or at 23/15 oC growth chamber (unreported).
In this study, our data showed that night temperature is the critical factor caused unstable CMS lines restore fertility. CMS hot pepper line ‘CCA 7243’ could restore fertility in the greenhouse and in the field while the night temperature was below 21 oC, and also could restore in the 20/15 oC phytotron (Fig. 4.5 A and Fig. 4.7). Plants of CMS sweet pepper line ‘CCA 7236’ restored fertility while night temperature was below 21oC or 17 oC, but plants hardly restored while day temperature below 18 oC (Fig.
4.6 A and Fig. 8). Besides, the fertility restoration of unstable CMS lines showed as a regular cycle, not always steady expressed. When night temperature went higher, both lines were reverted male sterile. Therefore, ‘CCA 7243’ and ‘CCA 7236’ both belonged to unstable CMS line.
In other CMS hot pepper line ‘CCA 7244’, plants had ever restored two times of fertility in the field of AVRDC (Fig. 4.6), but remained as male sterile in the greenhouse
41
and each phytotron (Fig. 4.5 B), and these results representing that ‘CCA 7244’ were less sensitive to temperature changes than ‘CCA 7243’. CMS sweet pepper line ‘CCA 7234’ always expressed male sterile even under a long period of lower night temperature. Therefore, ‘CCA 7244’ and ‘CCA 7234’ are stable CMS lines.
The reasons why unstable CMS plants could restore fertility as environment changes could be classified into two categories. One, the genetic background of CMS plants might be related to fertility restoration expressed under specific conditions. The level of male sterility expression of PCMS wheat lines was determined by the genotype of the nuclear donor (Murai, 2001a). Certain temperature could suppress or delay the recessive restorer gene action in some CMS plants, such as onion, alfalfa, pearl millet and rye (Kaul, 1988). The variation among CMS pepper lines in the expression of sterility presumably was caused by differences in number and nature of male-sterility modifying genes (Peterson, 1958; Shifriss, 1997). In cytological aspects, the PCMS wheat at floret development stage was sensitive to photoperiod, such as pistillate stamens under long-day condition (17h) transferring into normal stamens under short-day condition (13h) and producing functional pollens to self-pollination (Murai and Tunewaki, 1993). On the other hand, the breakdown during the process of microsporogenesis or microgametogenesis in CMS plants might block under the
42
specific conditions. Because malfunction might occur in early microsporogenesis in CMS pepper (Peterson, 1958), meiotic breakdown in unstable CMS pepper lines is either stopped or delayed when the temperature drop below the optimal temperature for pepper production and plants could produce viable pollens (Shifriss, 1997).
The fertile expression in maintainers was also affected by temperature. In hot pepper maintainers ‘PBC 483’ and ‘9907-9611’, the pollen viability maintained 60%
and higher in the 20/15 oC and 25/20 oC phytotron, but fewer flowers bloomed and pollen viability decreased in the 30/25 oC phytotron at (Fig. 4.5 C and D). However,
‘PBC 483’ and ‘9907-9611’ in the field still maintained higher fertility even if the day temperature was higher more than 30 oC but night temperature was lowerthan 25 oC (Fig.
4.6). The same results were in maintainer sweet pepper line ‘PBC 84 selex’ and
｀9847-4755’. (Fig. 4.7 C and D and Fig. 4.8). According to previous reports, the highest night temperature (24 oC ± 1) caused sweet pepper ‘Ma'or’ considerable blossom drop, but the highest tested day temperature (28 oC) did not cause increased blossom drop (Rylski and Spigelman, 1982). It could explain that the pollen viability of maintainers decreased in the 30/25 oC phytron at caused by high night temperature.
In tradition three-line CMS system, CMS plant was crossed by maintainer line to maintain their progeny, and crossed by restorer line to produce F1 seeds. The unstable
43
CMS plant which was sensitive to environment was also useful. The unstable CMS plants maintained their progeny by self-pollination while plants restored fertility, and produced hybrid seeds by cross-pollination with restorer while CMS plants remained sterile. It is so-called ‘two-line system’ (Murai and Tsunewaki, 1993; Murai et al, 2008;
Shifriss, 1997; Murai, 2001; Yang et al, 2006). Therefore, unstable CMS pepper lines used in this study also could develop into ‘two-line system’, and plants maintained their progeny from Dec. to Jun while night temperature was below 21 oC and produced hybrid seeds during Jul. to Nov. while night temperature was above 21 oC.
44
Table 4.1 The pedigree of CMS lines and maintainers from AVRDC-The World Vegetable Center.
CCA Code Pedigree hot/sweet
pepper
line of CMS system Stability of sterility CCA7243 Seungchon(cms)/8*Arunalu hot CMS Unstable
= CCA4758/PBC 483
CCA7244 Seungchon(cms)/8*9907-9611 hot CMS Stable
=CCA4759/9907-9611
PBC 483 Arunalu hot maintainer of CCA 7243 9907-9611 PBC 385 sle. hot maintainer of CCA 7244
CCA7236
PBC385-Aline/9*Jin's Sweetie
selex sweet CMS Unstable
CCA7234 PBC385-Aline/9*Mito Lee Selex sweet CMS Stable PBC 84 selex Jin's Sweetie sweet maintainer of CCA 7236
9847-4754 Mito Lee selex sweet maintainer of CCA 7234
45
Fig. 4.1 CMS and near-isogenic hot pepper plants grown in the AVRDC field.
(A) unstable CMS line ‘CCA 7243’; (B) near-isogenic line ‘PBC 385’ of ‘CCA 7243’; (C) stable CMS line ‘CCA 7244’; (D) near-isogenic line ‘9907-9611’ of
‘CCA 7244’.
Fig. 4.2 CMS and near-isogenic hot pepper flowers harvested from plants in the AVRDC field. (A)sterile flower of unstable CMS line ‘CCA 7243’(B) restored fertile flower of unstable CMS line ‘CCA 7243’; (C) fertile flower of near-isogenic line ‘PBC 385’; (D) sterile flower of stable CMS line ‘CCA 7244’; (E) fertile flower of near-isogenic line ‘9907-9611’.
46
Fig. 4.3 Sweet pepper plants grown in the AVRDC field. (A) unstable CMS line
‘CCA 7236’; (B) near-isogenic line ‘PBC 84sel’ of ‘CCA 7236’; (C) stable CMS line ‘CCA 7234’; (D) near-isogenic line ‘9847-4754’ of ‘CCA 7234’.
Fig. 4.4 CMS and near-isogenic sweet pepper flowers harvested from plants in the AVRDC field. (A)sterile flower of unstable CMS line ‘CCA 7236’; (B)fertile flower of near-isogenic line ‘PBC 84sel’; (C) sterile flower of stable CMS line ‘CCA 7234’; (D) fertile flower of near-isogenic line ‘9847-4754’ of ‘CCA 7234’.
47
Fig. 4.5 The trend of pollen viability percentage in hot pepper lines of (A) ‘CCA 7243’ (B) ‘CCA 7244’ (C) ‘PBC 483’
(D) ‘9907-9611’ in the greenhouse (GH) and in the phytotron of NTU at 30/25 oC, 25/20 oC, and 20/15oC from Apr. 29 to Jun. 29, 2007.
48
Fig. 4.6 The trend of pollen viability percentage in hot pepper lines in the field of AVRDC-The World Vegetable Center from December 7 to July 4.
0
CCA 7243 CCA7244 PBC 483 9907-9611
49
Fig. 4.7 The trend of pollen viability percentage in sweet pepper lines (A) ’CCA 7236’, (B) ‘CCA 7234’,
(C) ‘PBC 84 selex’, and (D) ‘9847-4754’ in the greenhouse (GH) and in the phytotron of NTU at 30/25 oC, 25/20 oC, and 20/15oC from Mar. 20 to Jun. 29, 2007.
50
Fig. 4.8 The trend of pollen viability percentage in sweet pepper lines in the field of AVRDC-The World Vegetable Center from December 7 to July 4.
0
CCA 7236 CCA 7234 PBC 84 selex 9847-4754
51