No abstract

Special purpose corn (Zea mays L.) cultivars and hybrids have been developed for manufacture of cob pipes. Little information is available concerning cultural practices most suited to the production of pipe corn. The objectives of the present investigation were to 1) determine whether plant density affects cob quality and 2) determine the simple correlations among cob quality traits.Tour corn (Zea mays L.) hybrids characterized by large cob size were evaluated at three densities at two locations in 2 years. Significant differences among hybrids were obtained for every trait studied and interactions among combinations of hybrids, years, locations, and plant spacing occurred frequently. Cob quality, as expressed by length, diameter, weight, and the length of cob exceeding a specified diameter, was improved significantly by reducing plant density. Similarly, crushing strength, weight, and density of 5.1‐cm cob sections increased significantly as plant density was reduced. Increased size, weight, density, and crushing strength would improve cob machinability and presumably increase the life expectancy of the pipes. We concluded that the pipe corn manufacturer would benefit appreciably by contracting pipe corn to be grown at relatively low plant densities to improve the quality and increase the frequency of acceptable cobs. Economic considerations will determine the appropriate plant density to achieve an acceptable balance between high quality cobs and grain yield per unit area.

Mass selection for resistance to corn earworm (Heliothis zea (Boddie)) was made in two corn, Zea mays L., populations (Synthetics C and S) grown in isolation for 10 generations during the period 1956 to 1965. Plantings were made on or about 15 June to enhance the chances for a high infestation of earworm. From each planting at least 1,000 ears were classified into three categories: (1) penetration of the earworm to the kernel resulting in damage, (2) earworm entry into the silk channel but no kernel damage, and (3) no evidence of earworm entry into the silk channel. Ears from class 2 were used for planting the subsequent cycleIn 1965, remnant seed of five cycles (spanning the 10 generations) for each synthetic was increased by sibpollinating approximately 200 plants. Evaluation tests were grown at two locations in 1966.Mass selection in both synthetics was effective. for Synthetic C the percentage of ears with kernel damage was reduced from 80.8% (1957) to 58.7% (1965), a reduction of 2.76% per generation. The percentage of ears with earworm damage for Synthetic S was reduced from 64.5% (1956) to 39.2% (1965). The average reduction per generation was 2.81%

E FFECTIVE selection for resistance to stalk lodging is one of the most difiqcult problems encountered in developing improved corn hybrids. Stalk lodging is a function of many variables, some genetic and others environmental, that interact from year to year and within specific growing seasons. Numerous morphological traits, anatomical structures, and inherent resistance to insects and plant pathogens are among the genetically conditioned aspects of lodging resistance. Selection for lodging resistance in corn has been frequently based on two primary objectives: selection for stalk rot resistance and selection for stronger stalks. Various disease ratings and mechanical means have been devised to test culm characteristics that could be highly correlated with field-lodging. These have usually provided a means of selecting stalks having increased strength and disease resistance. The importance of stalk-rotting organisms in increasing the frequency of stalk breakage has long been recognized. Pammel et al. (5) attributed much stalk breakage to weakness caused by fungus growth. Durrell (2), employing mechanical testing procedure, found that the breakingstrength of infe~ed stalks was reduced about half and attributed this loss to the assimilation of cellulose and small quantities of lignin by stalk-rotting pathogens. Koehler and Holbert (4) and Koehler (3) stated that Diplod~a maydis (Berk.) Sacc. (D. zeae (Schw.) Ldv.) accounted for many broken stalks in Illinois. Diplodia stalk rot also accounts for substantial stalk breakage in Missouri. Zuber and Grogan (8) devised a mechanical means evaluating stalk strength. Their crushing strength data were highly correlated with both stalk lodging and rind thickness. They concluded that rind-thickness determinations were a better means of evaluating stalk strength than were mechanical determinations of stalk-crushing strength. Rind thickness can be determined more rapidly and simply than crushing strength. The primary purpose of this investigation was to determine whether infection by D. mayd;s influences rind thickness and crushing strength of maize stalks. The possibility that complex effects of disease-inciting organisms may influence some of the morphological traits which condition resistance to stalk lodging was suggested by the results of Zuber et al. (9). They found that susceptibility to mayo/is and Gibberella zeae (Schw.) Petch. was correlated with certain chemical components of corn stalks. Physiological effects incited by infecting fungi may interfere or interact with the elaboration, transportation, degradation, or utilization of compounds entering into the formation of various morphological structures (9). As a consequence, any major effects of D. ma)'dis on rind thickness or crush