Abstract:

Kenaf is a fast growing annual plant that is harvested for its bast fibers. Heterosis in kenaf is remarkable and has been a research hotspot in the world. Zhou Ruiyang discovered a cytoplasmic male sterile mutant from a wild species UG93 in 2001 and first bred a cytoplasmic male sterile line of kenaf (UG93 CMS line) from it in 2004, which was highly resistant to anthracnose. To investigate the mechanism of microspore’s abortion of UG93 CMS lines in kenaf, a comparative study was conducted on microsporogenesis of two UG93 CMS lines named L23A and K03A with optical microscope. The observation showed that there were some similarities in the microspore’s abortive process between them: 1) Microspore’s abortion occurred at tetrad stage and mononuclear stage. 2) Extine of microspore disaggregated at mononuclear stage, with the protoplasm shrank or dissolved, and anthers became sterility. 3) The degeneration of middle layer was delayed, and more abnormality were found in tapetum, such as being vacuolated, cells fusion, hypertrophy and being broken away from the middle layer prematurely, etc. However, different abortive characters could be summarized as follows: 1) At the early and middle mononuclear stage, microspores of L23A developed well, but poorly developed extine which was thin and fragile, and smaller spinules of microspore were found in K03A. 2) Extine of microspore granulated quickly at late mononuclear stage in L23A, but it broken and dissolved gradually in K03A. 3) During the disaggregation of extine, the protoplasm of microspore shrank in L23A, with undistinguishable nuclear and cytoplasm, but it dissolved in K03A. It is suggested that the microspore’s abortive process between L23A and K03A is different and the abortion is related to abnormal behavior and no-function of tapetum.

Key words: Kenaf (Hibiscus cannabinus L.), Cytoplasmic male sterility, Microsporogenesis, Cytomorphology