In vivo interspecific pollination success between Pinus radiata,P. maximinoi, P. oocarpa and P. tecunumanii

The objective of the study was to investigate in vivo interspecific pollination success between Pinus radiata, P. maximinoi, P. oocarpa and P. tecunumanii.Pinus radiata was control pollinated with pollen lots of P.maximinoi, P. oocarpa and P. tecunumanii in a P. radiata seed orchard at Karatara(Southern Cape, South Africa).Pollination success was determined by counting the number of visible ovules, pollen grains inside and outside P.radiata ovules, as well as pollen tubes visible inside P.radiata ovules. Conelets were harvested and studied at eight time intervals, including 24 h after pollination, and weekly for 7 weeks after pollination. Histology studies with a standard fixation-dehydration-embedding sequence and paraffin wax method were used to determine the number of visible pollen grains inside versus outside the ovules and number of pollen tubes. Results indicated that pollen grains did sift through the cone scales within 24 h after pollination. However, P. radiata differed significantly (time by type of cross interaction) from the other three hybrid combinations in terms of number of visible ovules,visible pollen grains inside and outside of the ovules as well as pollen tubes, confirming limited interspecific hybridisation success. Future studies need to determine the percentage of fertile ovules in cross combination as a tool in predicting pollination success.