A greenhouse environment, heated and cooled with air drawn from a coal mine, was modified to reduce high humidity and dripping condensate. Polyethylene covered chambers, constructed within the mine-air greenhouse, were ventilated with mine-air, heated above mine-air temperature and ventilated with mine-air, or heated above mine-air temperature and ventilated with air drawn from outside the greenhouse. Heating the chambers above mine-air temperature did not reduce relative humidity significantly. However, polyethylene glazing on the chambers protected plants growing within the chambers from condensate dripping from the outer covering of the mineair greenhouse, which reduced the disease potential. Snapdragon and lettuce crops were produced in the chambers from early fall through spring. Snapdragon and lettuce grown in chambers ventilated with mine-air generally were of equal or better quality than plants produced in chambers provided with additional heat and ventilated with either mine-air or air drawn from outside the mine-air greenhouse.
The effects of in-row spacing (1.8, 3.0, and 4.3 m) and rootstock [seedling, Mailing Merton (MM) 111, MM 106, and Mailing (M) 7] on growth and yield of ‘Redspur Delicious’ (RS) and ‘Goldspur Golden Delicious’ (GS) apple (Malus domestica Borkh.) were studied over 14 years. Close in-row spacing generally reduced annual yield per tree of all scion-stock combinations. However, increased estimated yields per hectare resulted from close tree spacings, which compensated for the reduced yield per tree. RS/MM 106 generally had greater yield per tree than the others and exhibited greatest precocity. RS/seedling initially exhibited the lowest production per tree, although it eventually performed well. Of GS combinations, GS/M 7 generally performed best and GS/seedling poorest, although in early years the latter did well. Although a spacing × rootstock interaction on yield per tree or per hectare was not found in any year, significant spacing effects were first evident on clonal rootstocks (RS/MM 106, RS/M 7, GS/MM 111, GS/M 7). Cumulative production efficiency was affected by rootstock but not by spacing. RS and GS on MM 106 and M 7 were the most efficient, nearly twice that on seedling. Trunk cross-sectional area in 1984 was less on clonal than on seedling rootstocks. All combinations had smallest trunk size at the closest spacing.
Stem calli of various clones of apple (Malus domestica Borkh.) separated by filter paper, were grown on defined media to assess effects of one clone on growth of another in vitro. Certain clones affected the growth of the other when grown in the stock (callus in contact with media) or scion (on filter paper on stock callus) positions, or when placed on the media adjacent to each other (separated by filter paper). Both findings indicate the presence of mobile compounds from one clone capable of affecting growth of another clone.