Male Sterility in Sorghum bicolor (L.) Moench Induced by Low Night Temperature. I. Timing of the Stage of Sensitivity

Male sterility was induced in grain sorghum (CK 60 × Tx 415) by exposure of plants to five low- temperature nights (25°C day/ 10°C night). Sensitivity was greatest at the late archesporial cell- pollen mother cell development period, up to the leptotene stage of meiosis. Female fertility was unaffected. For a complete inflorescence, the period of sensitivity extended from flag leaf ligule emergence until the flag sheath had elongated to about 20 cm, a period of 6-7 days under 25°C day/ 20°C night conditions. Pollen development proceeded in an apparently normal manner following low temperature treatment, but was arrested just prior to maturation at the vacuolate two-celled microspore stage. Sterile pollen at anthesis was devoid of starch and had low levels of free proline. Assays of anther proline levels proved to give a reliable index of pollen maturation.