The Bur Enclosure of the Caryopses of Buffalograss as a Factor Affecting Germination

The seed-bur of buffalograss, Buchloe dactyloides (Nutt.) Engelm., consists of a tightly held rigid cluster four to five spikelets enclosed in thickened glumes. Germination of the bur is often difficult, requiring lengthy prechill treatments to attain maximum percentages. Caryopses contained in the bur germinate readily when extracted by hand, generally without additional pregermination treatment. The objective of this study was to evaluate the effect of the oil present in the bur enclosures on germination. Fresh seed burs were hammermilled to separate caryopses from their enclosures. Hulls or empty burs (100 samples) were further pulverized and then refluxed in 1,000 ml of distilled water overnight. The oil(s) present in the aqueous solution was evaporated in diethylether, and its properties characterized with infrared spectrophotometry and gas chromatography. A series of tests on the effect of the oil on germination and seedling growth was conducted. Treatments to counteract the effect of the bur enclosure on germination were also studied. The results showed that: 1) Empty burs contain 2.8% oil(s) by weight; 2) Caryopses extracted by hand germinate readily, the outer ginmes, by restricting water movement, may account for low laboratory germination of the seedburs; 3) Dipping the caryopses in the oil extract reduced germination by 47.2%; and 4) Dipping the root tips of healthy seedlings in the oil extract resulted in stunting plant growth. Prechilling at 5 to 10 C for 6 to 8 weeks or presoaking seed-burs in 5.25% sodium hypochlorite for 72 hours was sufficient to overcome the bur effect on germination. The length of both treatments needed to promote germination varied between seed lots studied. Subjecting the seed-burs to heat (drying) up to 70 C for 12 hours improved germination. Treatments beyond 70 C for more than 12 hours reduced seed viability.