Organogenesis of the Staminate and Pistillate Inflorescences of Pop and Dent Corns: Relationship to Leaf Stages¹

Abstract

Until recently, popcorn and dent corn (Zea mays L.) were considered analogous in their seasonal developmental patterns. Differences in the rates of seasonal floral development may be important in the relative susceptibility of the respective types of corn to stress. Although several researchers have considered that a relationship exists between the number of leaves emerged on a corn plant and inflorescence development, no intensive attempts to investigate floral development relative to leaf stage have been reported. This is an essential criterion if numeric staging systems are to be developed for use with regression techniques to model corn floral development relative to stress and consequent grain production. The objectives of this pilot study were to relate floral development to external leaf stage, and to compare the rate of floral development between a popcorn and its assumed analogue, a dent corn. Plants of two greenhouse‐grown corn cultivars, ‘Iopop 12’ and ‘B73 ✕ Mo17’, were sampled at intervals from emergence of the third leaf to that of the 13th leaf. The shoot apex and uppermost pistillate inflorescence were excised and examined fresh in a scanning electron microscope (SEM) or fixed and prepared for SEM examination using traditional techniques. Staminate and pistillate spikelet development in B73 ✕ Mo17 and in Iopop 12 followed a similar sequence; but, relative to leaf stages, Iopop 12 tended to lag one to two emerged‐leaf stages behind B73 ✕ Mo17. With respect to emerged‐leaf stages, B73 ✕ Mo17 and Iopop 12, respectively, developed as follows: tassel initiation at fourth vs. fifth, ear initiation at sixth vs. eighth, and pistillate silk formation at 11th vs. 13th. Staminate and pistillate spikelet organogenesis followed a similar sequence both within and between cultivars, with initiation of two bisexual florets and subsequent abortion of appropriate floral organs to form unisexual florets. One floret developed in each pistillate spikelet, whereas two developed in each taminate spikelet. Elongation of the apical dome to 0.4 mm was considered to be the most definitive indicator of tassel and ear initiation. The appearance of the ligule above the auricles of the previous leaf was considered the most definitive indicator of leaf‐blade emergence.

Analysis of inflorescence organogenesis in eastern gamagrass, Tripsacum dactyloides (Poaceae): the wild type and the gynomonoecious gsf1 mutant

“…However, in many cases the sessile spikelet appeared to arise proximal to the terminus of the original spikelet pair primordium. In fact, this organogenic pattern is common to annual (Sundberg and Orr, 1990) and perennial (Sundberg and Orr, 1986;Orr and Sundberg, 1994a) teosintes, but not maize (Cheng, Greyson, and Walden, 1983;Stevens et al, 1986;Sundberg et al, 1995;Sundberg and Orr, 1996). While both pairs of spikelets continued development along the distal portion of the rachis, pedicellate spikelets were aborted in the proximal (pistillate) region of the rachis (Fig.…”

“…This may support the idea that in T. dactyloides, like the teosintes (Sundberg and Orr, 1986;Camara-Hernandez and Gambino, 1992) and wildtype maize (Bonnett, 1953), the sessile spikelet is a branch of the pedicellate. Although maize produces spikelet pair primordia that divide to produce paired spikelets, subse-quent abortion of the pedicellate spikelet to produce solitary mature spikelets does not occur in either modern (Cheng, Greyson, and Walden, 1983;Stevens et al, 1986), or land race (Sundberg, LaFargue, and Orr, 1995;Sundberg and Orr, 1996) maize ear formation. 52).…”

Organogenesis of Fascicled ear mutant inflorescences in maize (Poaceae)

“…Early inflorescence organogenesis produces bisexual flowers (florets) in both inflorescence types; subsequent developmental events, i.e., arrest and abortion of floral organ primordia, shift the inflorescence to a unisexual morphology (Bonnett, 1953;Stevens et al, 1986). Early inflorescence organogenesis produces bisexual flowers (florets) in both inflorescence types; subsequent developmental events, i.e., arrest and abortion of floral organ primordia, shift the inflorescence to a unisexual morphology (Bonnett, 1953;Stevens et al, 1986).…”

“…In the transition of the vegetative meristem to the inflorescence meristem, the key aberrant organogenic feature of Fas inflorescences is the perturbation of the shoot apex: Fas shifts the direction of growth (apex width doubles its height) away from the normal transition of the vegetative meristem into an inflorescence (Cheng, Greyson, and Walden, 1983;Stevens et al, 1986;Sundberg, LaFargue, and Orr, 1995;Sundberg and Orr, 1996), and promotes a bifurcation of the abnormal broad transition meristem into two primary inflorescence axes each with a terminal apical meristem. In the transition of the vegetative meristem to the inflorescence meristem, the key aberrant organogenic feature of Fas inflorescences is the perturbation of the shoot apex: Fas shifts the direction of growth (apex width doubles its height) away from the normal transition of the vegetative meristem into an inflorescence (Cheng, Greyson, and Walden, 1983;Stevens et al, 1986;Sundberg, LaFargue, and Orr, 1995;Sundberg and Orr, 1996), and promotes a bifurcation of the abnormal broad transition meristem into two primary inflorescence axes each with a terminal apical meristem.…”

“…Succeeding organogenesis of the fascicled central spike showed a typical wild-type pattern of staminate development (Cheng, Greyson, and Walden, 1983;Stevens et al, 1986;Irish and Nelson, 1993;Sundberg, LaFargue, and Orr, 1995;Sundberg and Orr, 1996).…”