Interested Members of the University Community are invited to attend the Final Oral Examination for the Degree of Doctor of Philosophy of  Victor Hugo Gonzalez of the Department of Plant Agriculture

Date: Thursday, July 25^th 2019
Time: 10:00 AM
Location: Room 202, Crop Sciences Building

Thesis Title: “TIMING OF STRESS AND YIELD DETERMINATION IN MAIZE (ZEA MAYS L.) “

Advisory Committee:   
Dr. Clarence Swanton  (Advisor) 
Dr. Liz Lee
Dr. Hugh Earl
Dr. Lewis Lukens                                                

Examination Committee:
Dr. Clarence Swanton
Dr. Liz Lee
Dr. Bill Deen
Dr. Bao-Luo Ma (External - Agriculture and Agri-Food Canada)
Dr. David Wolyn (Chair)

ABSTRACT

Yield loss in maize (Zea mays L.) is well known to be caused by abiotic and biotic stresses. Previous studies have focused, primarily, on the determination of yield loss as a result of stress occurring during the critical reproductive stages, that is, around silking and the grain fill period. No studies have assessed yield loss caused by differing stresses that occur early during the vegetative phase. Studies were conducted during 2012-13 under controlled and field conditions at two locations in Ontario, Canada. Early season stresses (i.e., up to V9 stage of growth) included drought, light quality (red to far red) and early high-plant density while high plant density was considered a season long stress. In this thesis, the hypothesis was tested that if yield is reduced in response to early season stress, then, resource capture and resource utilization will be reduced proportionally. The relationship between plant dry matter and floret number follows the classic relationship with a minimum dry matter level required and a plateau. Not all stresses impacted these relationships in the same manner. These results confirm that floret number in maize is established well in advance of flowering and also suggests that floret number is related to plant dry weight sampled between V7 to V9-10 stage of growth. Yield loss in the drought and early high-plant density stress treatments, was caused by reductions in dry matter accumulation and kernel number. Growth rates around silking were reduced and flowering delayed in response to early season stress which explained reductions in kernel set. While ASI was only lengthened by early high density, HI remained unchanged in response to early season stress. Season-long high plant density stress resulted in reduced plant dry matter, and kernel number. Plants presenting low dry matter accumulation in each stage of growth exhibited lower floret and kernel number. Barren plants at maturity showed very low or no dry matter accumulation during the grain filling period. Overall, early season stress reduced resource capture only, while season long stress defined as high plant density reduced both resource capture and utilization.   

Gonzalez, V.H., E.A. Lee, L.L. Lukens, and C.J. Swanton. 2019. The relationship between floret number and plant dry matter accumulation varies with early season stress in maize ( Zea mays L .). F. Crop. Res. 238(March): 129–138. doi: 10.1016/j.fcr.2019.05.003.

Gonzalez, V.H., J.O. Mackenzie, M. Tollenaar, and E.A. Lee. 2019. Physiological Mechanisms Underlying Genetic Improvement in Sink Establishment and Plant-to-Plant Variability in Maize Journal: Crop Sci.: Accepted.

Gonzalez, V.H., M. Tollenaar, A. Bowman, B. Good, and E.A. Lee. 2018. Maize yield potential and density tolerance. Crop Sci. 58: 472–485. doi: 10.2135/cropsci2016.06.0547.

Reid, A., V.H. Gonzalez, P.H. Sikkema, E.A. Lee, L. Lukens, and C.J. Swanton. 2014. Delaying Weed Control Lengthens the Anthesis-Silking Interval in Maize. Weed Sci. 62: 326–337. doi: 10.1614/WS-D-13-00099.1.

Echarte, L., A. Della Maggiora, D. Cerrudo, V.H. Gonzalez, P.E. Abbate, A. Cerrudo, V.O. Sadras, and P.A. Calviño. 2011. Yield response to plant density of maize and sunflower intercropped with soybean. F. Crop. Res. 121: 423–429. doi: 10.1016/j.fcr.2011.01.011.