Chromosome knob patterns in maize and annual teosinte

The work of Kato, Longley, Blumenschein, McClintock and Brown has provided us with abundant data on chromosome knob frequencies for most regions and subdivisions of maize and teosinte. A reanalysis of these data has been part of a 15-year survey of variation patterns in the genus Zea, based on iterative analysis of the many data tables. It has been possible to describe groupings of taxa (collections and races, Table 1) and of variables (knob presence or frequency, Table 2).

Table 1. The population samples used to calculate the averages in Table 3. Generally prior classifications can be used, but Balsas is divided because of significant differences between the northwest and southeast ends of its range. There is remarkably little difference between the Guanajuato and Michoacan populations of Central Plateau teosinte.
 
Taxonomic unit Samples used for averages
   
Zea luxurians Cutler 202 A; Wilkes 51764, 51839, 51850
   
Zea mexicana  
Huehuetenango Wilkes San Antonio Huixta, Tzibaj, Monajil
Balsas, SE Kato K-69-13; Beadle 1972 El Salado (3 collections); Wilkes 47335
Balsas, NW Kato K-67-13, -14; Wilkes 47890, 47942
Central Plateau from Guanajuato: Kato K-89-1, -2, -7. -10, -11;

from NE Michoacan: Kato K-69-3, -4, -5, -6, -8, -9; Wilkes 45470

Chalco Kato K-65-2, K-66-1, K-67-1, -2, -3, K-68-1, -2, -4,

-6, K-69-12; 1970 T-1, T-2, T-3, T-4

Nobogame Wilkes Nobogame (2 collections)
   
Zea mays  
Olotillo Yucatan 37; Guatemala 108, 130, 131, 134, 314, 322,

600, 744, 769, 875

Nal-tel Campeche 18, 29, 37, 102; Yucatan 7, 102, 129, 146;

Guatemala 52, 115, 145, 260

Pollo Cundinamarca 401; Pollo Segregaciones
Conico Guanajuato 2; Hidalgo 22; Mexico 3, 182, 207; Tlaxcala 1
Coroico Bolivia 992, 1035, 1063, 1071
Chulpi Chile 435, 438; Ecuador 387, 434, 598, 697

Table 2. Knobs arranged into sets according to their intercorrelations and listed in the order of their average frequency. A is the Andean set and is the only one present in dozens of high altitude races. C1 and C2 contain the most frequent knobs in the Caribbean and Middle American lowland races. One or two more sets of internal knobs could be defined for the latter region, usually found in low frequency.
 
Set Knobs
Terminal knobs  
T1 2S3, 1S3, 6L5, 4L3, 10L3, 2L2, 7L3, 5L2, 9L3, 8L3
T2 4S2, 3S2, 5S2
T3 9S, 7S, 8S
   
Internal knobs  
C1 5L1, 8L1, 4L1, 3L1, 2L1, 6L2
C2 1S2, 8L2, 9L2
A 7L1, 6L3

In maize there is great contrast between Andean-Amazonian races with high frequencies of knobs at the 7L1 and 6L3 positions (Knob set A) and Caribbean-Middle American races with four sets of knobs in varying frequencies (Sets A, C1, C2 and T3). Within each of these regional subdivisions, frequencies vary greatly.

In annual teosinte the major variation is between the Guatemalan teosintes with many knobs terminal on long and short chromosome arms and Mexican races with few terminal knobs and many internal knobs. However, tassels and spikelets of Zea luxurians of southeast Guatemala differ greatly from those of race Huehuetenango of northwest Guatemala which has the Z. mexicana form (Table 3). Mexican annual teosintes differ more subtly; all are fairly similar in knob patterns to Caribbean-Middle American maizes, with Nobogame the least so. Chalco seems to be the most like maize in knob pattern, as well as plant form. Central Plateau, including several geographic populations with somewhat different knob frequencies, is much like Chalco in several ways. There is considerable variation in the Balsas race, resolvable into a northwest group of populations, in southern Michoacan, with levels of knobs 7S, 8S, 4L1, 2L1, 1S2, 3L2, 7L2 and 3S1 higher than in a southeast group near Chilpancingo, Gro. (El Salado, Mazatlan, etc.). The latter group has shorter plants with more tillers and narrower leaves than the Michoacan group. Nobogame of Chihuahua in northwest Mexico has low knob frequencies and several traits indicative of introgression with local maize. Several teosinte populations are not on Table 3. A Central Balsas group (Kato's no. 8-11 and 16), a western state of Mexico group (no. 32-37), and collections from eastern Michoacan (no. 49-54) are intermediate between two or more of the other groups.

Table 3. Chromosome knob frequencies, by sets of knobs, using data from Kato (1975, Mass. Agr. Exp. Sta. Bull. 635), Longley and Kato (1965, CIMMYT Res. Bull. 1) and McClintock (in Ramirez E. at al., 1960, Races of Maize in Bolivia; in Timothy et al., 1961, Races of Maize in Chile; in Timothy et al., 1963, Races of Maize in Ecuador). Few knob positions are occupied in all members of a race. The population samples used and the knob set compositions are listed in Tables 1 and 2. N' is the number of population samples used per race, and N" is the number of plants used for the knob counts.
 
    Percent of knob positions filled
  Terminal sets Internal sets
Taxonomic unit N':N" T1 T2  T3 C1 C2 A
               
Zea luxurians 4:18 73 69 0 0 0 0
               
Zea mexicana              
Northwest Guatemala              
  Huehuetenango 3:26 53 76 75 0 0 0
Central Mexico              
  Balsas, SE 5:25 0 20 27 44 18 86
  Balsas, NW 4:25 0 20 63 67 40 60
  Central Plateau 12:59 0 2 13 60 42 42
  Chalco 14:33 0 8 36 75 27 52
Northwest Mexico              
  Nobogame 2:16 0 0 3 20 4 3
               
Zea mays              
Caribbean pattern              
  Olotillo 11:35 0 0 39 94 79 97
  Nal-tel 12:64 0 1 37 89 61 98
  Pollo 2:15 0 0 27 74 20 63
  Conico 6:49 0 0 16 39 10 41
Andean pattern              
  Coroico 4: 6 0 0 0 7 0 100
  Chulpi 6: 9 0 0 0 0 0 67

There is considerable correlation between many of the knobs--7S correlates with 9S, 8L2 with 9L2, etc. The "sets" of Tables 2 and 3 are groups of knobs demonstrating similar trends for at least the major types of maize and teosinte. The correlations between knobs are important in two ways--a reduced set of factors seems to be responsible for their frequencies and many fewer measurements are needed to derive the same patterns. Knobs have varying degrees of independent control, so they have varying importance in taxonomic and evolutionary models. In low frequencies there are 19 other knobs, all with some geographical-racial relationships--two terminal knobs are limited to northwest Guatemala teosinte (average frequency of 13%), seven internal knobs are shared by Mexican teosinte and Caribbean-Middle American maize (averages, 26% and 7%, respectively), and ten internal knobs are restricted to Mexican teosinte (average, 4%).

Robert McK. Bird


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