Canopy Responses Of Zoysiagrass Genotypes Under Progressive Dry Down.

Determining an efficient process for screening drought responses of turfgrasses would facilitate breeding for drought resistant species and cultivars. Measurements of transpiration rate, stomata regulation and root development could serve as criteria for separating turfgrasses with different responses under drought. In this study, eight zoysiagrass genotypes identified from previous research to differ in their transpiration rates and stomata regulation were evaluated under a progressive dry down. The objectives of the study were to: 1) compare the performance of these genotypes under both greenhouse and field drought conditions, 2) explore the mechanisms associated with canopy response differences and establish reliable criteria for screening, and, 3) correlate visual ratings with canopy spectral reflectance measurements. Among the eight zoysiagrasses were four genotypes of Zoysia japonica (‘JaMur’, BA182, DALZ4360, and DALZ5269-24) and four genotypes of Z. matrella (‘PristineFlora’, ‘Zeon’, BA374, and BA336). Canopy net photosynthesis (P_n), canopy transpiration rate, canopy spectral reflectance (NDVI), visual ratings and percent green cover (PGC) were measured. NDVI and PGC of Zoysia spp. were positively correlated with visual quality during dry down. Among Z. matrella cultivars, BA336 and Zeon maintained higher visual quality, NDVI and PGC compared to PristineFlora and BA374. Among Z. japonica cultivars, DALZ4360 performed consistently worse (low visual quality, NDVI and PGC) having a low transpiration rate, medium breaking point and poor rooting. BA336 was shown to maintain higher P_n, higher root:shoot ratio, and extensive and deep rooting. Zeon was found to reduce its P_n early during dry down, but was able to maintain its performance during the dry down with its low transpiration rate and by having more roots deeper in the soil profile. In Zeon, drought tolerance mechanisms such as osmotic adjustment, membrane stability and protein accumulation may play a significant role for maintaining its performance. DALZ5269-24 had greater visual quality and higher P_n in the greenhouse dry down through development of more roots deeper in the soil profile. Z. japonica entries did not exhibit as consistent dry down responses as Z. matrella between field and greenhouse experiments.