Breeding of a creeping bentgrass (Agrostis palustris Huds.) cultivar 'CY-2' and characteristics of summer bentgrass decline of 'CY-2' turf

This study summarizes the breeding process of a creeping bentgrass cultivar 'CY-2' and the growth and performance characteristics of 'CY-2' turf under limited or non fungicide conditions in summer. The results obtained were as follows. 1. Breeding of a creeping bentgrass cultivar 'CY-2' 146 clones of creeping bentgrass were originally selected for disease resistance, insect resistance, low anthocyanin appearance during the winter periods and heavy summer heat stress based on pesticide-free conditions. 9 parental clones were finally selected from the 146 primarily selected clones based on resistance to two major diseases, dollar spot disease and brown patch. Selection was also based on low anthocyanin appearance during the winter. One other clone, previously selected for its resistance to these diseases and low anthocyanin appearance, was added to 9 clones to create 3 polycross groups for breeding. The degree of resistance to the two major diseases and levels of anthocyanin appearance were examined in experimental polycross group cultivars CY- I, II, and III. Each group consisted of 5 or 6 parental clones according to the turf characteristics. In comparison to existing cultivars, 'L-93', 'PennA-1', 'PennA-4', 'Putter' and 'Penncross' resistance to these diseases in the experimental polycross groups were higher, and anthocyanin appearance during winter periods in the experimental polycross groups were lower, respectively. 'CY-2', consisting of 6 clones of CY-II and one clone of CY- III, was evaluated to be the best new bred cultivar in total performance in regards to low susceptibility to the major two diseases, low anthocyanin appearance. 2. The characteristics of growth and the mineral nutrient concentration in the leaf tissue of 'CY-2' in summer Putting quality tended to be high in order of 'CY-2', 'L-93' and 'Penncross' grown as putting green under limited or non fungicide conditions in summer. The calcium (Ca) and magnesium (Mg) concentrations of 'Penncross' were distinctly the highest of the three cultivars, 'CY-2', 'L-93' and 'Penncross,' and the K concentrations of 'CY-2' and 'L-93' tended to be high. The K/Mg ratio and K/Ca ratio tended to be high in order of 'CY-2,' 'L-93,' and 'Penncross,' and this tendency was consistent among the years. 3. The relationship between mineral concentration, electrical conductivity (EC) and pH in the late fall dew water on the 'CY-2' turf The additional effects of matrix modifiers on the measurement of the mineral elements in late fall dew on two creeping bentgrass cultivars by atomic spectrometry method were observed. The calcium carbonate as matrix modifier for the determination of potassium (K) showed higher values than without modifier. The lanthanum chloride as matrix modifiers for the determination of Ca showed significantly higher values than without modifier. The lanthanum chloride as matrix modifiers for the determination of Mg showed no effects on them. However, the concentration of all minerals in the dew water of 'Penncross' was higher than 'CY-2'. The co-relationship between EC and all mineral concentration values with matrix modifiers was significantly high. 4. The influence of disease injury and fungicide application on mineral concentration in the dew water on the 'CY-2' turf The number of spots caused by the dollar spot disease in the non fungicide treated plot was larger and the rate of disease area of the brown patch was higher than in the fungicide treated plot. The number of spots caused by the dollar spot disease in 'Penncross' was greater than the number of spots in 'CY-2'. The EC of the dew water adhering to the leaf surfaces of the non fungicide treated plot showed the tendency to be higher than EC in the fungicide treated plot. Moreover, the EC of 'CY-2' tended to be lower than EC of 'Penncross'. K, Ca, and Mg concentration in dew adhering to the turf surface in the non fungicide treated plot were all higher than the fungicide treated plot, and their concentrations in dew water from 'Penncross' were higher than the values of 'CY-2'. From these analysis results, concentrations of K, Ca, and Mg leaching to adhering dew on the turf surface of the creeping bentgrass differ among cultivars. Moreover, it was suggested that the leaching increases in connection with the damage of stem and leaf by diseases occurrence. 5. The relationship between turf quality, EC of dew on turf surface and electrolyte leakage (EL) from leaf blade of 'CY-2' in summer The number of spots caused by the dollar spot disease and the turf area damaged by brown patch in summer were fewer in 'CY-2' than in 'Penncross'. The turf quality of 'CY-2' was also higher than that of 'Penncross'. The EC of dew water on the turf surface of 'CY-2' were constantly lower than those of 'Penncross'. The difference between EC in the two creeping bentgrass cultivars may be related to the difference between the turf qualities. Differences in EL from the leaf blade of the cultivars were not significant in 'CY-2.' The Mg and Ca concentrations of the shaking extract solution and the leakage of these components from the leaf blade with a low cutting height of 3.7 mm were lower than those in 'Penncross'. This explains the difference in EC, EL, and turf quality between the two creeping bentgrass cultivars. The deterioration of turf in summer causes increased rate of mineral leakage from the leaves, and this can be detected by the increased EC of dew water on the turf surface or higher Mg and Ca concentrations of the shaking extract solution of the leaf blade with a low cutting height. These factors help us in characterizing the differences in heat and disease tolerance between cultivars.