The influence of phytohormones, wheat ovary co-culture, and temperature stress on anther culture response of watermelon (Citrullus lanatus L.)

The anther culture response of Citrullus lanatus L. was studied to evaluate the effect of growth regulators and wheat ovary-conditioned medium in Charleston Gray cultivar and the effect of temperature pretreatment in Crimson sweet cultivar. Callus-mediated embryogenesis was induced on Murashige and Skoog (MS) medium supplemented with 2, 4-dichlorophenoxyacetic acid (2,4-D) and a-naphthaleneacetic acid alone as well as 2,4-D in combination with N6-benzylaminopurine/kinetin (BAP/KN). Optimal percentage of embryogenic calli (EC) and mean number of embryos per anther (ME/A) were induced on MS medium supplemented with 2.0 mu M 2, 4-D and 1.5 mu M BAP in cultivar of Charleston Gray. In this cultivar, the inclusion of 10 wheat ovaries in the induction medium significantly increased the percentage of EC and ME/A up to 2.5- and 3-fold when compared with that in the control, respectively. Low-temperature pretreatment of flower buds (4 degrees C for 2 and 5 days) and cultured anthers (4 degrees C for 4 and 8 days) were tested in Crimson sweet cultivar and best response in terms of % EC and ME/A was obtained with pretreatment of cultured anthers at 4 degrees C for 4 days and flower buds at 4 degrees C for 2 days. Also, heat pretreatments of the cultured anthers at 30 degrees C for 7 and 32 degrees C for 2 days produced the highest percentage of EC compared to control and other heat pretreatments in Crimson sweet cultivar. The highest frequency of ME/A was obtained from cultured anthers incubated at 32 degrees C for 2 days. Embryos germinated into plantlets on MS medium containing 2.22 mu M BAP, 3 % sucrose, and 0.8 % agar. The root tips of 12 regenerated plantlets were analyzed for ploidy level, of which 10 have been haploids.