Discovery and identification of litchi male sterile line MS1

Abstract：【Objective】Male sterile line plays an important role in cross breeding and heterosis utilization of plants. In recent years, we discovered a new litchi male sterile line and named it MS1. In this study, we identified its sterile characters by various methods, so as to provide the foundation for the following research and use.【Methods】Using the grafted litchi male sterile line MS1 and male fertile line D13 as experimental materials. Using Sony α77 camera and self- made macro lens to take photos of flower organs, setting the same shooting distance and exposure to ensure the actual size and color were reflected. The different appearances of litchi male sterile line MS1 and the male fertile line D13 were analyzed. Using 1% safranine solution with 75% alcohol for anther staining. After staining, using 10% sucrose solution with distilled water to reduce the surface tension. Then the anthers were ground and observed under a microscope. The paraffin section was carried out for observation of the anther structure. The samples was dehydrated with 70%, 80%, 95% and 100% alcohol for 15 minutes each, then transparentized with xylene for 15 minutes twice, and an 8 µm permanent section was made. The microscope was used to magnify 100-200 times for observation and photography. The silicone dryer was used to dry the anthers for 72 hours, after coating and spraying gold, the samples were observed under the SEM. 1% sucrose solution was used to dissolve the prepared anther powder of D13 and MS1, MS1 female spikes were sprayed with the two solutions respectively and bagged up. The number of fruit setting was counted 30 days after the pollination.【Results】(1) In appearance, litchi male sterile line MS1 had a small number of male flowers, anthers, and its anther color was milky white, which could easily fall off without cracking. The number of anthers of MS1 was 4-6, while the number of anthers of D13 was 6-12. Occasionally some spikes of MS1 only come out with female flowers. A few anthers mightcrack when mature, but no pollen grains could be observed. The litchi fertile line D13 had a large number of male flowers and its anther color was faint yellow, which would easily cracke when mature and release a large amount of pollen; (2) Under the SEM, the female and male anthers of the litchi male sterile line MS1 were thin and small, with many sunken surfaces, and most of them did not crack when mature. The anther chambers of the litchi male fertile line D13 cracked when mature where there were a large number of pollen grains; (3) After aniline safranine staining, no pollen grains were found in the anther grinding fluid of the litchi male sterile line MS1, while a large number of different color of pollen grains were found in the anther grinding fluid of the litchi male fertile line D13; (4) Paraffin sections showed that there was no pollen grain in the anther chamber of the litchi male sterile line MS1, with normal epidermis, endothecium and vascular bundle, and the anther chamber formed a cavity and did not crack when mature. The litchi fertile line D13 had normal epidermis, endothecium, and vascular bundle. The Pollen grains were released from the cracking stomium of the anther chamber when mature; (5) The litchi male sterile line MS1 had a failure in fruiting with self-pollination, while litchi male sterile line MS1 had normal fruit setting (8.2 fruits of each spike averagely) when it was pollinated with the pollens of the litchi male fertile line D13.【Conclusion】Compared with the normal fertile line, litchi male sterile line MS1 was a male sterile of pollenfree with normal epidermis, endothecium and vascular bundle, and its anther chamber formed a cavity and did not crack when mature.